When your Mitsubishi Electric system stops and shows a code, that code is the system telling you roughly where the problem is. Roughly is the key word. A fault code points in a direction, it rarely names the exact fix. Find your system below, tap your code, and it will take you straight to what it means and what to do.
Before you try anything: the only DIY steps that are ever safe are switching the system off at the isolator (and waiting 20 to 30 minutes), cleaning or checking filters, checking the controller settings and batteries, and keeping the outdoor unit clear. Anything behind a panel, anything electrical, and anything involving refrigerant or gas is licensed work. If a code below says switch off and call, please take it at its word.
How to read the tables: 🟢 means there is a safe first step worth trying. 🟡 means book a service, the system needs a technician. 🔴 means switch the system off at the isolator and call us on (02) 4760 0100.
Mr Slim P Series (A-control) — inverter-era ducted, cassette, ceiling-suspended and wall-mounted light commercial
Where the code shows: Two-character code on the wired wall controller (PAR series). Many codes also flash on service LEDs (LED1 green / LED2 red — flash counts noted per code; the source doc does not say which board carries these LEDs) and map to a 4-digit M-NET code when on a central controller..
Tap your code: EAEbECE0E1E2E3E4E5E6E7E8E9EDEFP1P2P4P5P6P8P9F1F2F3F4F5F7F8F9FAU1U2U3U4U5U6U7UAUdUEUFUHUL
| Code | What it means | What to do |
|---|---|---|
| EA | The indoor and outdoor units are wired to each other incorrectly, or more indoor units are connected than the outdoor unit allows. Checked at the outdoor unit. M-NET equivalent 6844. |
🟡 Book a service and quote the code, this is a wiring or setup issue that needs a technician. |
| Eb | The wiring between the indoor and outdoor unit is crossed or disconnected. Checked at the outdoor unit. Wrong cable size/spec is a known cause. M-NET equivalent 6845. |
🟡 Book a service and quote the code, this is a wiring or setup issue that needs a technician. |
| EC | The units could not finish their start-up handshake in time. Start-up time over; electrical interference or wrong cable spec are cited causes. M-NET equivalent 6846. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| E0 | The wall controller is not receiving a signal from the unit. Remote controller transmission error (receiving side). LED1 2 flashes / LED2 3 flashes. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| E1 | A fault with the wall controller itself or how it has been grouped. On grouped or twinned systems, controller addressing and master-wiring are the usual suspects. |
🟡 Book a service and quote the code. |
| E2 | A fault with the wall controller or its addressing. Same checks as E1, grouping/addressing, and on twinned systems the controller must be wired to the master indoor unit. |
🟡 Book a service and quote the code. |
| E3 | The wall controller cannot transmit its signal to the unit. Remote controller transmission error (transmitting side). LED1 2 flashes / LED2 3 flashes. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| E4 | The indoor unit is not receiving the wall controller's signal. LED1 2 flashes / LED2 3 flashes. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| E5 | The indoor unit cannot transmit its reply to the wall controller. LED1 2 flashes / LED2 3 flashes. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| E6 | The indoor and outdoor units have lost communication with each other. Classic after power is restored in the wrong order (outdoor before indoor); interference on the S1/S2 line (e.g. from a drain pump wired into it) is another cause. M-NET equivalent 6840. LED1 2 flashes / LED2 2 flashes. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| E7 | Communication fault between the indoor and outdoor units (detected at the indoor unit, transmitting side). Service checks include 12/24 V DC on S2–S3 and any condensate pump wired at the indoor unit. LED1 2 flashes / LED2 2 flashes. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| E8 | The outdoor unit is not receiving the indoor unit's signal (S2/S3 line). Powering up in the wrong order is a common cause, indoor should come on before outdoor. M-NET equivalent 6840. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| E9 | The outdoor unit cannot transmit to the indoor unit (S2/S3 line). M-NET equivalent 6841. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| ED | Circuit boards inside the outdoor unit have lost serial communication with each other. Can be caused by an M-NET interface board that is not seated correctly. M-NET equivalent 403. LED1 2 flashes / LED2 5 flashes. |
🟡 Book a service and quote the code. |
| EF | A non-specific communication error, usually caused by electrical interference. Also logged as an M-NET transmission error. Manufacturer guidance is a 30-second power-down of the outdoor unit. M-NET equivalent 6607. LED1 2 flashes / LED2 4 flashes. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| P1 | The return-air temperature sensor is not reading properly or has come unplugged. TH1 thermistor open/short circuit. LED1 4 flashes / LED2 1 flash. |
🟡 Book a service and quote the code. |
| P2 | The indoor pipe (liquid line) temperature sensor is not reading properly or has come unplugged. TH2 thermistor open/short circuit. LED1 4 flashes / LED2 1 flash. |
🟡 Book a service and quote the code. |
| P4 | The condensate drain sensor is faulty or disconnected. DS open/short circuit. LED1 4 flashes / LED2 2 flashes. |
🟡 Book a service and quote the code. |
| P5 | Condensate water is not draining away, the level in the tray is high, pointing to a failed drain pump or a blocked drain. LED1 4 flashes / LED2 2 flashes. |
🟡 Switch the unit off if you can see any water dripping, and book a service. |
| P6 | The indoor coil froze up in cooling or overheated in heating, almost always an airflow problem. Frost/overheat protection. Dirty filters, a blocked return-air path or a fan fault are the usual causes. LED1 4 flashes / LED2 3 flashes. |
🟢 Clean or check the return-air filters and make sure vents are open, then power-cycle at the isolator with a 20–30 minute wait. If the code returns, book a service. |
| P8 | Pipe temperatures are not changing the way they should, often a sign the system has lost refrigerant. Abnormal pipe temperature; can also be a temperature sensor mounted out of position. LED1 4 flashes / LED2 4 flashes. |
🔴 Switch the system off at the isolator and call for service. |
| P9 | The coil (condenser/evaporator) temperature sensor is faulty or has come off the board. TH5 thermistor open/short circuit. LED1 4 flashes / LED2 1 flash. |
🟡 Book a service and quote the code. |
| F1 | The three-phase power supply is connected in the wrong phase order. Reverse phase detection. M-NET equivalent 4103. LED1 1 flash / LED2 1 flash. |
🟡 Book a service and quote the code, this points to a power-supply problem. |
| F2 | One phase (L3) of the three-phase power supply is missing. Open-phase detection; protection devices in the supply may have opened. M-NET equivalent 4102. LED1 1 flash / LED2 1 flash. |
🟡 Book a service and quote the code, this points to a power-supply problem. |
| F3 | The low-pressure switch circuit is open, a disconnected plug or failed contact. 63L connector. Mapped to M-NET 5202 in the source. LED1 1 flash / LED2 2 flashes. |
🟡 Book a service and quote the code. |
| F4 | The compressor's internal overheat thermostat circuit is open. 49C connector open or contact failure. Mapped to M-NET 4124. LED1 1 flash / LED2 2 flashes. |
🟡 Book a service and quote the code. |
| F5 | The high-pressure switch circuit is open, a disconnected plug or failed contact. 63H switch. Mapped to M-NET 5201 in the source. LED1 1 flash / LED2 2 flashes. |
🟡 Book a service and quote the code. |
| F7 | The phase-detection circuit on the outdoor board has failed. Usually a faulty outdoor PCB. M-NET equivalent 4118. LED1 1 flash / LED2 3 flashes. |
🟡 Book a service and quote the code. |
| F8 | The outdoor board's input circuit is faulty. Points to a defective outdoor board. LED1 1 flash / LED2 3 flashes. |
🟡 Book a service and quote the code. |
| F9 | Two or more protection-device circuits are open at the same time. M-NET equivalent 4119. LED1 1 flash / LED2 2 flashes. |
🟡 Book a service and quote the code. |
| FA | Either the L2 supply phase is missing or the compressor overcurrent relay circuit is open. 51CM connector / thermal relay. M-NET equivalent 4108. LED1 1 flash / LED2 2 flashes. |
🟡 Book a service and quote the code. |
| U1 | The system shut down because refrigerant pressure went too high. 63H high-pressure switch tripped (M-NET 1302; LED1 3 flashes / LED2 2 flashes). Blocked outdoor coil, outdoor fan failure, a system blockage or dirty indoor filters in heating are the listed causes. The blog source also lists U1 as 'direct cut operation' on some models. |
🟡 Check the filters are clean and the outdoor unit has clear space around it, then power-cycle at the isolator with a 20–30 minute wait. If it trips again, book a service. |
| U2 | The compressor ran too hot, often because the system is low on refrigerant. High discharge temperature (M-NET 1102; LED1 3 flashes / LED2 1 flash). Can also be the compressor's internal thermostat (49C) tripping, a faulty thermistor, or very high ambient conditions. |
🔴 Switch the system off at the isolator and call for service. |
| U3 | The discharge temperature sensor is open or short circuit. Mapped to M-NET 5104 in the source. LED1 3 flashes / LED2 5 flashes. |
🟡 Book a service and quote the code. |
| U4 | The outdoor temperature sensor is open or short circuit. Mapped to M-NET 5105 in the source. LED1 3 flashes / LED2 5 flashes. |
🟡 Book a service and quote the code. |
| U5 | The inverter's heat sink is running too hot. TH8 heat-sink sensor (M-NET 4230; LED1 3 flashes / LED2 6 flashes). Poor airflow around the heat sink, missing silicone paste or a faulty thermistor are cited causes. |
🟡 Book a service and quote the code. |
| U6 | The compressor is drawing too much electrical current. Compressor overcurrent / overload cut-off (M-NET 4250; LED1 3 flashes / LED2 4 flashes). Needs inverter output tests and electrical checks. |
🔴 Switch the system off at the isolator and call for service. |
| U7 | Discharge superheat is too low, the refrigerant metering is not right. Points to the TH4 sensor reading or LEV (expansion valve) operation. M-NET equivalent 1520. LED1 3 flashes / LED2 1 flash. |
🟡 Book a service and quote the code. |
| UA | Compressor overcurrent, the terminal relay has operated. Not in the 2011 compendium, but confirmed in independent A-control lists: compressor over current (terminal relay operation). |
🔴 Switch the system off at the isolator and call for service. |
| Ud | The unit stopped on overheat protection. Source gives no further cause. Confirmed as 'over heat protection' in ARMA and official Mitsubishi lists. |
🟡 Book a service and quote the code. |
| UE | High refrigerant pressure caused by a closed service (ball) valve. Typically seen at commissioning when a stop valve was left shut. Confirmed as 'high pressure error (ball valve closed)' in ARMA and official Mitsubishi lists. |
🔴 Switch the system off at the isolator and call for service. |
| UF | The compressor is locked and cutting out on overcurrent, at start-up or while running. Shown for both start-up locked and operating locked in the A-control list; the official Mitsubishi list gives 'compressor overcurrent interruption (when compressor locked)'. |
🔴 Switch the system off at the isolator and call for service. |
| UH | The current sensor is giving faulty readings. Confirmed as 'current sensor error' in ARMA and official Mitsubishi lists. |
🟡 Book a service and quote the code. |
| UL | Refrigerant pressure is abnormally low, a possible leak. Confirmed as 'abnormal low pressure' in independent A-control lists; a possible refrigerant leak. |
🔴 Switch the system off at the isolator and call for service. |
Mr Slim P Series (K-control) — older R22-era ducted and cassette light commercial
Where the code shows: Code shown on the K-control wired remote controller..
| Code | What it means | What to do |
|---|---|---|
| E0 | The wall controller and indoor unit are not communicating. Transmit/receive signal error. Can also be wrong group or master/slave settings (CN40, SW2, SW6). |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| P1 | The intake (return-air) temperature sensor is faulty. TH1 thermistor, roughly 6.4 kilohm at 20°C when healthy. |
🟡 Book a service and quote the code. |
| P2 | The pipe/coil temperature sensor is faulty. TH2 thermistor, roughly 6.4 kilohm at 20°C when healthy. |
🟡 Book a service and quote the code. |
| P3 | Signal transmission error within the system. Same checks as E0, communication between indoor unit and controller, or group/master-slave settings (CN40, SW2, SW6). |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the code comes back, book a service. |
| P4 | The condensate drain sensor is faulty. Sensor resistance, connection and continuity checks. |
🟡 Book a service and quote the code. |
| P5 | The drain overflow protection has tripped, condensate is not getting away. Blocked drain or tray, drain pump failure, or a faulty sensor. |
🟡 Switch the unit off if you can see any water dripping, and book a service. |
| P6 | The indoor coil's frost or overheat protection tripped, usually an airflow problem. Detected by the indoor coil sensor; lack of airflow or a refrigerant charge problem are the listed causes. |
🟢 Clean or check the return-air filters and make sure vents are open, then power-cycle at the isolator with a 20–30 minute wait. If the code returns, book a service. |
| P7 | System address setting error. CN40, SW2 and SW6 settings; possible board fault. |
🟡 Book a service and quote the code. |
| P8 | The outdoor unit has a fault, indoor temperatures are not changing after start-up. No indoor temperature change after about 9 minutes of running. Listed causes: outdoor unit tripped, refrigerant charge problem, lack of airflow, or TH2 faulty/badly mounted. |
🔴 Switch the system off at the isolator and call for service. |
Mr Slim K-control — PUH-EK outdoor units (LED diagnostics)
Where the code shows: LEDs LD1–LD8 on the outdoor unit control board: steady ON means a normal operating status, flashing means the fault listed here..
Tap your code: LD1 (flashing)LD2 (flashing)LD3 (flashing)LD4 (flashing)LD5 (flashing)LD6 (flashing)LD7 (flashing)LD8 (flashing)
| Code | What it means | What to do |
|---|---|---|
| LD1 (flashing) | Three-phase power is connected in the wrong phase order. Reverse-phase detect. Steady LD1 just means the compressor is being called (normal). |
🟡 Book a service and quote the code, this points to a power-supply problem. |
| LD2 (flashing) | A supply phase is missing, or a protection component's circuit is open. Open-phase detect. The compendium also lists CH, 52C, 21S4, SV, 63H and 26C open circuits under LD2. Steady LD2 = heating call (normal). |
🟡 Book a service and quote the code. |
| LD3 (flashing) | The outdoor coil/pipe sensor is open or short circuit. May be disconnected, or an outdoor board fault. Steady LD3 = 63H1 operating (normal). |
🟡 Book a service and quote the code. |
| LD4 (flashing) | The high-pressure switch has tripped. 63H2 operation, investigate high-pressure causes or a disconnected switch. Steady LD4 = compressor running (normal). |
🟡 Check the outdoor unit has clear space and airflow around it and the filters are clean, then book a service if the fault returns. |
| LD5 (flashing) | The compressor overcurrent relay tripped, the compressor is locked or pulling too much current. 51CM operation; power supply also worth checking. Steady LD5 = outdoor fan running (normal). |
🔴 Switch the system off at the isolator and call for service. |
| LD6 (flashing) | The thermal switch tripped, can point to low refrigerant. 26C operation; check for low refrigerant level or a disconnected switch. Steady LD6 = 4-way (reversing) valve energised (normal). |
🔴 Switch the system off at the isolator and call for service. |
| LD7 (flashing) | Coil overheat protection, the coil passed 67°C, usually from poor airflow at the outdoor unit. TH3 overheat protection; fan motor or thermistor faults are the cited causes. Steady LD7 = bypass valve open (normal). |
🟡 Make sure the outdoor unit has clear space and airflow around it, then book a service if the fault returns. |
| LD8 (flashing) | The outdoor board's input circuit is defective. Source says replace the outdoor board. Steady LD8 = crankcase heater on (normal). |
🟡 Book a service and quote the code. |
City Multi VRF (R22 / R407C / R410A generations; includes BC controller and Lossnay-linked codes)
Where the code shows: Four-digit code on the local remote controller, central controller or outdoor unit service display. The source lists applicability per code by refrigerant generation (R22 / R407C / R410A) and for Lossnay units..
Tap your code: 04031102111111121113120212041205121112141216121712191221124313011302136813701402150015011505250025022503260041004101410241034106410841154116412442104220422542304235424042454250425542605101510251035104510551065107510851095110511151125113511451155116520152025203530053015401570162016202660066016602660366076608683068316832683368346840684168446845684671007101710271057106710771107111711371177130
| Code | What it means | What to do |
|---|---|---|
| 0403 | Two circuit boards inside the unit have stopped talking to each other over the serial link. Check the inverter error detail for which two boards; transformer, bus voltage and inter-board cables are the listed checks. Shown as 403 in the source. |
🟡 Report the code to your service contractor, this needs a technician. |
| 1102 | The compressor's discharge gas passed 110°C, commonly a refrigerant shortage. A faulty discharge thermistor can also trigger it. |
🔴 Switch the system off and call your service contractor straight away. |
| 1111 | Low refrigerant pressure/temperature fault. Listed checks: TH2/TH3/TH4 thermistors, gas charge, indoor fan, heat exchanger and filters. Source gives identical text for 1111, 1112 and 1113. |
🔴 Switch the system off and call your service contractor straight away. |
| 1112 | Low refrigerant pressure/temperature fault. Listed checks: TH2/TH3/TH4 thermistors, gas charge, indoor fan, heat exchanger and filters. Source gives identical text for 1111, 1112 and 1113. |
🔴 Switch the system off and call your service contractor straight away. |
| 1113 | Low refrigerant pressure/temperature fault. Listed checks: TH2/TH3/TH4 thermistors, gas charge, indoor fan, heat exchanger and filters. Source gives identical text for 1111, 1112 and 1113. |
🔴 Switch the system off and call your service contractor straight away. |
| 1202 | Early warning of a high discharge-temperature fault (precursor to 1102). | 🟡 Report the code to your service contractor, this needs a technician. |
| 1204 | Early warning fault on the heat-exchanger gas temperature sensors. Thermistors 10a and 10b. |
🟡 Report the code to your service contractor, this needs a technician. |
| 1205 | Early warning fault on the TH5 pipe temperature sensor. | 🟡 Report the code to your service contractor, this needs a technician. |
| 1211 | Early warning fault on the TH2 temperature sensor. | 🟡 Report the code to your service contractor, this needs a technician. |
| 1214 | Early warning fault on the inverter heat-sink temperature sensor. THHS thermistor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 1216 | Early warning fault on the TH7 temperature sensor. | 🟡 Report the code to your service contractor, this needs a technician. |
| 1217 | Early warning fault on the TH8 temperature sensor. | 🟡 Report the code to your service contractor, this needs a technician. |
| 1219 | Early warning fault on the TH9 temperature sensor. | 🟡 Report the code to your service contractor, this needs a technician. |
| 1221 | Early warning fault on the TH6 temperature sensor. | 🟡 Report the code to your service contractor, this needs a technician. |
| 1243 | Early warning fault on the TH10 temperature sensor. | 🟡 Report the code to your service contractor, this needs a technician. |
| 1301 | Refrigerant pressure read under 1 bar just before start-up, low charge or a sensor fault. 63L operation detected via the low-pressure sensor. |
🔴 Switch the system off and call your service contractor straight away. |
| 1302 | The system tripped on high refrigerant pressure. Trip thresholds about 29 bar (R407C) or 38 bar (R410A); the high-pressure sensor is compared against gauge pressure. |
🟡 Report the code to your service contractor, this needs a technician. |
| 1368 | Pressure sensor PS1 at the BC controller is reading incorrectly. Compared against the outdoor unit's SW1 pressure display. |
🟡 Report the code to your service contractor, this needs a technician. |
| 1370 | Pressure sensor PS3 at the BC controller is reading incorrectly. Compared against the outdoor unit's SW1 pressure display. |
🟡 Report the code to your service contractor, this needs a technician. |
| 1402 | Early warning of a high-pressure fault (precursor to 1302). | 🟡 Report the code to your service contractor, this needs a technician. |
| 1500 | The system has too much refrigerant in it, compressor superheat is abnormally low. Detected via the TH4 discharge thermistor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 1501 | The compressor shell is running hot, refrigerant shortage suspected. On computer-room systems, too little indoor capacity running can also cause it. |
🔴 Switch the system off and call your service contractor straight away. |
| 1505 | Suction pressure abnormal, the compressor pulled a vacuum. Listed causes: a blockage, a closed service valve or a faulty low-pressure sensor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 2500 | Not enough water flow detected in the water circuit. Applies to water-circuit models. |
🟡 Report the code to your service contractor, this needs a technician. |
| 2502 | Water is building up in the indoor unit's drain tray during cooling (temperature-sensor detection). Checks: sensor circuits open/closed and drain pump operation. |
🟡 Report the code to your service contractor, this needs a technician. |
| 2503 | The drain tray float switch tripped, condensate is not draining away. Checks: float switch circuit and drain pump operation. |
🟡 Report the code to your service contractor, this needs a technician. |
| 2600 | A water leak was detected from the humidifier. | 🟡 Report the code to your service contractor, this needs a technician. |
| 4100 | Compressor overcurrent protection tripped on a Mr Slim unit connected via an M-NET interface. Inverter or compressor at fault. |
🔴 Switch the system off and call your service contractor straight away. |
| 4101 | Compressor overcurrent protection tripped on a Mr Slim unit connected via an M-NET interface. Inverter or compressor at fault. Source gives identical text for 4100 and 4101. |
🔴 Switch the system off and call your service contractor straight away. |
| 4102 | A supply phase is missing (open phase). Power supply, noise filter, wiring and fuse checks. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4103 | Supply phases are connected in the wrong order (reverse phase). Also flags a lost phase through the noise filter, a blown fuse, or the high-pressure switch open at power-on. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4106 | Fault in the transmission-line power supply. Wiring, high current, incorrect voltage on the transmission line, or the M-NET board. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4108 | Overcurrent trip on a direct-on-line compressor. Power supply, contactor and compressor checks. |
🔴 Switch the system off and call your service contractor straight away. |
| 4115 | The power supply to the unit is abnormal. Power, fuses, connections and PCB checks. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4116 | Fan motor fault on an indoor or Lossnay unit. Fan motor and board checks. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4124 | The compressor's internal thermal switch circuit is open (Mr Slim unit on M-NET). 49C thermal switch; reset and check pressures and airflow. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4210 | Compressor overcurrent problem. Inverter balance, compressor and inverter checks. |
🔴 Switch the system off and call your service contractor straight away. |
| 4220 | The inverter's DC bus voltage is too low (under about 289 V DC). Usually a mains supply issue. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4225 | DC voltage is too low on the fan inverter. Checks: about 300 V DC at the diode stack (CNVdc) and the mains supply to the outdoor unit. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4230 | The inverter's heat sink is overheating. Blocked air duct, failed inverter fan or a faulty thermistor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4235 | The fan inverter's heat sink overheat protection tripped. Reduced airflow through the heat sink, a fan motor problem, or the THHS thermistor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4240 | Overcurrent protection, high current sustained for more than 10 minutes. Inverter balance and heat-sink airflow checks. |
🔴 Switch the system off and call your service contractor straight away. |
| 4245 | Overcurrent protection tripped, possibly a faulty current sensor. ACCT sensor; a healthy one reads about 280 ohm across pins 1–2 and 3–4. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4250 | Overcurrent protection, an inverter power-module fault or a locked compressor. IPM problem or compressor lock; inverter balance checks. |
🔴 Switch the system off and call your service contractor straight away. |
| 4255 | Problem with the inverter's cooling fan. With a high-static fan fitted, switch SW3-9 must be on. |
🟡 Report the code to your service contractor, this needs a technician. |
| 4260 | Early warning of inverter heat-sink overheating. Reduced heat-sink airflow, a fan motor problem, or the THHS thermistor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5101 | A temperature sensor on an indoor or outdoor unit has failed. The fault-code address identifies which unit and sensor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5102 | A temperature sensor on an indoor or outdoor unit has failed. The fault-code address identifies which unit and sensor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5103 | A temperature sensor on an indoor or outdoor unit has failed. The fault-code address identifies which unit and sensor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5104 | A temperature sensor on an indoor or outdoor unit has failed. The fault-code address identifies which unit and sensor. For indoor faults the source also says confirm switch SW7-3 is off. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5105 | Temperature sensor TH5 is open or short circuit. Check whether the thermistor has come off the board. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5106 | Temperature sensor TH6 is open or short circuit. Check whether the thermistor has come off the board. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5107 | Temperature sensor TH7 is open or short circuit. Check whether the thermistor has come off the board. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5108 | Temperature sensor TH8 is open or short circuit. Check whether the thermistor has come off the board. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5109 | Temperature sensor TH9 is open or short circuit. Check whether the thermistor has come off the board. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5110 | Temperature sensor TH10 is open or short circuit. Check whether the thermistor has come off the board. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5111 | BC controller temperature sensor TH11 is open or short circuit, or off its pipe. | 🟡 Report the code to your service contractor, this needs a technician. |
| 5112 | A BC controller temperature sensor is open or short circuit, or off its pipe. The compendium prints 'TH10' here, a misprint: official City Multi service handbooks (PURY series) give 5112 as the bypass outlet temperature sensor (TH12) fault on the BC controller. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5113 | A BC controller temperature sensor is open or short circuit, or off its pipe. Sensor number not given in the source. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5114 | A BC controller temperature sensor is open or short circuit, or off its pipe. Sensor number not given in the source. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5115 | BC controller temperature sensor TH15 is open or short circuit, or off its pipe. | 🟡 Report the code to your service contractor, this needs a technician. |
| 5116 | BC controller temperature sensor TH16 is open or short circuit, or off its pipe. | 🟡 Report the code to your service contractor, this needs a technician. |
| 5201 | Pressure sensor fault at the outdoor unit or BC controller. SW1 pressure readouts compared against gauge, per the fault-code address. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5202 | Pressure sensor PS2 in the BC controller is faulty. | 🟡 Report the code to your service contractor, this needs a technician. |
| 5203 | Pressure sensor PS3 in the BC controller is faulty. | 🟡 Report the code to your service contractor, this needs a technician. |
| 5300 | A Mr Slim unit on the network reported a current-sensor (UH) fault. M-NET translation of the Mr Slim A-control UH code. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5301 | Current sensor fault on the inverter. ACCT or DCCT sensor; the inverter error details identify which. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5401 | Humidity/temperature sensor fault. Connector CN30 for the humidity sensor. |
🟡 Report the code to your service contractor, this needs a technician. |
| 5701 | The drain-tray float switch connector has come loose. Float switch and connector CN4F on the indoor unit. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6201 | Communication error on the TB7 transmission line. Voltage abnormality or a short on the line. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6202 | Hardware error in the transmission processor. Electrical noise or a short on the M-NET cable. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6600 | Two or more units on the network have been given the same address. Fixed by correcting the repeated address. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6601 | Polarity or voltage problem on the M-NET transmission line. No voltage or a short circuit on the line. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6602 | Transmission processor hardware error, interference or a polarity problem on TB7. | 🟡 Report the code to your service contractor, this needs a technician. |
| 6603 | The network bus is jammed, often something wired into TB7 that belongs on TB3. | 🟡 Report the code to your service contractor, this needs a technician. |
| 6607 | A unit on the network stopped answering while the system was running. No response received back from the unit; often follows a power interruption. |
🟢 If there has been a power interruption, turn the system off at the isolator, wait 20–30 minutes and restore power. If the code returns, call your service contractor. |
| 6608 | Network communication dropped out, voltage loss or electrical noise on the line. | 🟢 If there has been a power interruption, turn the system off at the isolator, wait 20–30 minutes and restore power. If the code returns, call your service contractor. |
| 6830 | The indoor unit and MA remote controller are not communicating. Checks: controller connections, 12 V DC on the controller line, and that the controller is not set as a sub controller. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6831 | The MA remote controller is not receiving. Checks: TB15 connections; removing the controller while the indoor unit is powered can trigger it. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6832 | MA remote controller communication fault. Checks: cable length (max 500 m), cable type, connections, and the main/sub controller setting. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6833 | MA remote controller communication fault (transmitting side). Checks: cable length (max 500 m), cable type, connections, and the main/sub controller setting. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6834 | MA remote controller communication fault (receiving side). Checks: cable length (max 500 m), cable type, connections, and the main/sub controller setting. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6840 | A Mr Slim unit on the network reported an indoor/outdoor communication fault (its E6/E8 code). M-NET translation of Mr Slim A-control E6/E8. |
🟢 If there has been a power interruption, turn the system off at the isolator, wait 20–30 minutes and restore power. If the code returns, call your service contractor. |
| 6841 | A Mr Slim unit on the network reported an indoor/outdoor communication fault (its E7/E9 code). M-NET translation of Mr Slim A-control E7/E9. |
🟢 If there has been a power interruption, turn the system off at the isolator, wait 20–30 minutes and restore power. If the code returns, call your service contractor. |
| 6844 | A Mr Slim unit on the network reported a wiring/connection fault (its EA code). Mis-wiring, loose inter-connecting cables or interference. M-NET translation of Mr Slim A-control EA. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6845 | A Mr Slim unit on the network reported a wiring fault (its Eb code). Mis-wiring, loose cables, interference, or wrong cable size/spec. M-NET translation of Mr Slim A-control Eb. |
🟡 Report the code to your service contractor, this needs a technician. |
| 6846 | A Mr Slim unit on the network failed to finish starting up in time (its EC code). Interference or wrong cable size/spec. M-NET translation of Mr Slim A-control EC. |
🟢 If there has been a power interruption, turn the system off at the isolator, wait 20–30 minutes and restore power. If the code returns, call your service contractor. |
| 7100 | The total indoor unit capacity exceeds what the outdoor unit allows. Limits: 150% of index on R2 series, 130% on Y series. |
🟡 Report the code to your service contractor, this needs a technician. |
| 7101 | A capacity setting switch is set wrong. SW2 on indoor units, SW5 on YHM-A outdoor units (SW3-10 on older equipment). |
🟡 Report the code to your service contractor, this needs a technician. |
| 7102 | The number of connected units does not match what the system expects. M-NET voltage loss (short or break), no power at the BC controller, a wrong SW5 setting, or the wrong BC box type. |
🟡 Report the code to your service contractor, this needs a technician. |
| 7105 | An outdoor unit or BC controller address is set wrong. | 🟡 Report the code to your service contractor, this needs a technician. |
| 7106 | Attribute setting error. SW3-1 setting on a GUF (Lossnay heat-recovery) unit. |
🟡 Report the code to your service contractor, this needs a technician. |
| 7107 | BC controller port setting error. Too much capacity on a single port, wiring/SW2 setting, a wrong SW14 setting, or wrong unit assignment when using multiple BC boxes. |
🟡 Report the code to your service contractor, this needs a technician. |
| 7110 | Connection-count setting switch SW5-7 is set incorrectly. | 🟡 Report the code to your service contractor, this needs a technician. |
| 7111 | The system expects a temperature sensor in a remote controller that is missing or has failed. SW1-1 on with no controllers fitted, or a faulty remote controller. |
🟡 Report the code to your service contractor, this needs a technician. |
| 7113 | Function setting error, a wrong switch setting or wrong resistors fitted. SW5 setting or resistors on YHM-A units. |
🟡 Report the code to your service contractor, this needs a technician. |
| 7117 | Model setting error, a switch or resistor configuration is wrong. SW5 setting or wrong resistors fitted. |
🟡 Report the code to your service contractor, this needs a technician. |
| 7130 | Incompatible equipment is connected to the network. Example given: a split with a MAC-399 interface wired onto the TB5 line instead of TB7. |
🟡 Report the code to your service contractor, this needs a technician. |
M-NET central controller — Lossnay ventilation fault codes (A-series)
Where the code shows: Two-character code on the central controller; the matching 4-digit M-NET code and LED1 (green) / LED2 (red) flash counts are noted per code..
| Code | What it means | What to do |
|---|---|---|
| A0 | Two or more Lossnay ventilation units share the same network address. M-NET 6600. LED1 2 flashes / LED2 5 flashes. Fixed by re-addressing the units and resetting power. |
🟡 Book a service and quote the code, this is a setup issue that needs a technician. |
| A2 | Hardware fault in a Lossnay unit's transmission processor. M-NET 6602. LED1 2 flashes / LED2 5 flashes. Communication wiring or a Lossnay board fault. |
🟡 Book a service and quote the code. |
| A3 | The network line stayed busy, nothing could transmit for 8 minutes. M-NET 6603. LED1 2 flashes / LED2 5 flashes. Check M-NET connections (TB7/TB3). |
🟡 Book a service and quote the code. |
| A6 | Communication processor error, the Lossnay unit's address never got transmitted. M-NET 6606. LED1 2 flashes / LED2 5 flashes. Check M-NET voltage. |
🟡 Book a service and quote the code. |
| A7 | No acknowledgement signal came back over the network. M-NET 6607. LED1 2 flashes / LED2 5 flashes. Wiring range exceeded or a faulty M-NET converter. |
🟡 Book a service and quote the code. |
| A8 | A unit on the network stopped responding. M-NET 6608. LED1 2 flashes / LED2 5 flashes. Wiring range, a faulty converter or the wrong cable type. |
🟡 Book a service and quote the code. |
M-series residential (MSZ) — MSZ-AP hi-wall indoor unit blink codes (live faults)
Where the code shows: Blink count of the OPERATION INDICATOR lamp on the indoor unit's display (the top lamp). When a fault is detected the unit stops, the indoor fan switches off and the lamp blinks in bursts separated by a 2.5-second pause; count the flashes in one burst. Standard MSZ wireless remotes show no letter-number code, the blinks are the code. Extracted from the MSZ-AP15-71 VF/VG(K) service manuals; AU retail models MSZ-AP22-50VGD/VGKD are the same platform..
Tap your code: Blinking continuously (0.5 s on / 0.5 s off)2 blinks per burst3 blinks per burst4 blinks per burst5 blinks per burst6 blinks per burst7 blinks per burst14 blinks or more per burstLamp stays lit but the outdoor unit will not runTop lamp lit and lower lamp blinking
| Code | What it means | What to do |
|---|---|---|
| Blinking continuously (0.5 s on / 0.5 s off) | The indoor and outdoor units have stopped talking to each other, from a connection problem or a lost signal. Serial signal from the outdoor unit not received for 6 minutes. Also appears when an indoor unit that was once paired with a different outdoor-unit generation needs its stored history cleared (low-standby-power pairing note in the manual). |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the light blinks again, book a service. |
| 2 blinks per burst | A temperature sensor inside the indoor unit (room air or coil sensor) is not reading properly. Indoor coil thermistor or room temperature thermistor open or short circuit, checked every 8 seconds during operation. |
🟡 Book a service and quote the blink count. |
| 3 blinks per burst | The indoor fan motor is not reporting its speed back, the fan or its drive has a problem. No rotational-frequency feedback signal during indoor fan operation. |
🟡 Book a service and quote the blink count. |
| 4 blinks per burst | The indoor unit's control board has an internal memory fault. Nonvolatile memory on the indoor electronic control PCB cannot be read; board replacement is the listed remedy. |
🟡 Book a service and quote the blink count. |
| 5 blinks per burst | The outdoor unit keeps tripping its compressor protection straight after starting. Compressor stopped by overcurrent protection or start-up failure protection 3 consecutive times within 1 minute of starting. A closed service (stop) valve is a listed check. |
🔴 Switch the system off at the isolator and call for service. |
| 6 blinks per burst | A temperature sensor in the outdoor unit is not reading properly. Outdoor thermistor open or short circuit during compressor operation (discharge, defrost, fin, board, ambient or heat-exchanger sensor; the outdoor unit's own board LED tells the technician which one). |
🟡 Book a service and quote the blink count. |
| 7 blinks per burst | The outdoor unit's control electronics have an internal memory fault. Nonvolatile memory of the inverter PCB or the outdoor electronic control PCB cannot be read. |
🟡 Book a service and quote the blink count. |
| 14 blinks or more per burst | The outdoor unit has a fault outside the standard list. Listed checks are the stop valve and the 4-way valve; the exact fault is pinned down with the failure mode recall function. |
🟡 Book a service and quote the blink count. |
| Lamp stays lit but the outdoor unit will not run | The outdoor unit's control board cannot read its memory, so the outdoor unit refuses to start while the indoor unit looks normal. Same nonvolatile-memory fault as 7 blinks, indicated with the lamp lit instead; confirmed by the LED on the outdoor unit's boards. |
🟡 Book a service and mention that the indoor light stays on while the outdoor unit never starts. |
| Top lamp lit and lower lamp blinking | Usually not a fault. On a multi-head (MXZ) system the rooms are asking for opposite modes, and on demand-response models the electricity network has temporarily capped the unit. MXZ: indoor units set to COOL (including DRY) and HEAT at the same time; the first unit started has priority. AU MUZ-VGD demand models show the same indication during a DRM 2 or DRM 3 demand-response event (AS/NZS 4755.3.1), which ends by itself. |
🟢 On a multi-head system, set every indoor unit to the same mode on the remote. If your unit is on a demand-response program, wait for the event to end. If neither applies, book a service. |
M-series residential (MSZ) — remote-control self-check (failure mode recall), indoor unit faults
Where the code shows: Service self-check run from the wireless remote: with power on, hold OPERATION SELECT and the TEMP up button while pressing RESET on the remote, release RESET, keep holding the other two for 3 seconds until every LCD segment shows, then point the remote at the unit and press OFF/ON. The stored fault replays as blink bursts (with beeps) on the indoor OPERATION INDICATOR lamp. IMPORTANT: blink counts in this mode differ from the live fault blinks, and the mode must be released afterwards (power off, power on, press RESET on the remote) or the unit cannot operate properly..
Tap your code: 1 blink per burst (recall mode)2 blinks per burst (recall mode)3 blinks per burst (recall mode)11 blinks per burst (recall mode)12 blinks per burst (recall mode)
| Code | What it means | What to do |
|---|---|---|
| 1 blink per burst (recall mode) | A room temperature sensor fault is stored in the unit's memory. Room temperature thermistor open or short circuit was detected during operation. |
🟡 Book a service and quote the blink count. |
| 2 blinks per burst (recall mode) | An indoor coil temperature sensor fault is stored in the unit's memory. Indoor coil thermistor (main or sub) open or short circuit was detected during operation. |
🟡 Book a service and quote the blink count. |
| 3 blinks per burst (recall mode) | A communication dropout between the indoor and outdoor units is stored in the unit's memory. Serial signal from the outdoor unit was not received for up to 6 minutes. |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the light blinks again, book a service. |
| 11 blinks per burst (recall mode) | An indoor fan motor fault is stored in the unit's memory. No rotational-frequency feedback for 12 seconds after the indoor fan motor was operated. |
🟡 Book a service and quote the blink count. |
| 12 blinks per burst (recall mode) | An indoor control board memory fault is stored in the unit's memory. Nonvolatile memory of the indoor electronic control PCB could not be read; board replacement is the listed remedy. |
🟡 Book a service and quote the blink count. |
M-series residential (MSZ) — remote-control self-check (failure mode recall), outdoor unit faults
Where the code shows: Second stage of the same remote self-check: with the recall function active, press the TEMP up button so 25°C is set to interrogate the outdoor unit. Outdoor faults replay on the indoor OPERATION INDICATOR lamp as a 3-second ON (no beep) followed by the blink burst with beeps; it can take up to a minute to start. Counts differ from live fault blinks. Matching patterns also show on the outdoor inverter-board LED for technicians..
Tap your code: 1 blink per burst (outdoor recall)2 blinks per burst (outdoor recall)3 blinks per burst (outdoor recall)4 blinks per burst (outdoor recall)5 blinks per burst (outdoor recall)6 blinks per burst (outdoor recall)7 blinks per burst (outdoor recall)8 blinks per burst (outdoor recall)9 blinks per burst (outdoor recall)10 blinks per burst (outdoor recall)11 blinks per burst (outdoor recall)14 blinks per burst (outdoor recall)16 blinks per burst (outdoor recall)
| Code | What it means | What to do |
|---|---|---|
| 1 blink per burst (outdoor recall) | A communication fault at the outdoor unit's end is stored in memory. No usable signal from the inverter PCB for 3 minutes, or 30 consecutive corrupted frames (signal sent as 0, received as 1). |
🟢 Turn the system off at the isolator, wait 20–30 minutes, then turn it back on. If the light blinks again, book a service. |
| 2 blinks per burst (outdoor recall) | The compressor's overcurrent protection tripped repeatedly right after starting. Overcurrent cut-out operated 3 consecutive times within 1 minute of the compressor starting. Listed remedies: reconnect the compressor connector, inverter/compressor checks, stop valve. |
🔴 Switch the system off at the isolator and call for service. |
| 3 blinks per burst (outdoor recall) | An outdoor temperature sensor fault is stored in memory. A thermistor shorted or opened while the compressor ran (discharge, defrost, fin, board, ambient or outdoor heat-exchanger sensor; the outdoor board LED blink count 1 to 4 identifies which). |
🟡 Book a service and quote the blink count. |
| 4 blinks per burst (outdoor recall) | The inverter saw too much current going into its power module, or the compressor would not start cleanly. Large current into power module IC700 (outdoor LED 11 blinks), or distorted compressor current waveform, compressor start-up failure protection (outdoor LED 12 blinks). |
🔴 Switch the system off at the isolator and call for service. |
| 5 blinks per burst (outdoor recall) | The compressor ran too hot, which commonly points to low refrigerant. Discharge temperature thermistor exceeded 116°C and the compressor stopped; restart is allowed once it reads 100°C or less 3 minutes later. Listed checks: refrigerant circuit and amount, LEV (expansion valve). |
🔴 Switch the system off at the isolator and call for service. |
| 6 blinks per burst (outdoor recall) | The system tripped on high-pressure protection, detected through coil temperatures. Indoor coil thermistor over 70°C in HEAT mode, or defrost thermistor over 70°C in COOL mode. Listed checks: refrigerant circuit and amount, stop valve. |
🟡 Check the filters are clean and the outdoor unit has clear space around it, then book a service if it happens again. |
| 7 blinks per burst (outdoor recall) | The outdoor unit's power electronics ran too hot. Fin temperature thermistor on the inverter heat sink exceeded 75–86°C (AP25-60) / 75–80°C (AP71), or the board temperature thermistor exceeded 72–85°C / 70–75°C. Listed checks: around the outdoor unit, its air passage, the outdoor fan motor. |
🟡 Make sure the outdoor unit has clear space and airflow around it, then book a service if the fault returns. |
| 8 blinks per burst (outdoor recall) | The outdoor fan motor kept stopping just after start-up. Outdoor fan stopped 3 times in a row within 30 seconds of fan start-up. Listed checks: outdoor fan motor, inverter PCB. |
🟡 Book a service and quote the blink count. |
| 9 blinks per burst (outdoor recall) | Either the inverter board's memory failed, or there is a short circuit in the inverter power module or compressor windings. Outdoor board LED 5 blinks = nonvolatile memory cannot be read (replace inverter PCB); 6 blinks = interface short circuit at the power module (IC700) output / shorted compressor winding. |
🔴 Switch the system off at the isolator and call for service. |
| 10 blinks per burst (outdoor recall) | The compressor's discharge stayed abnormally cold, the refrigerant metering is not right. Discharge temperature thermistor read 50°C or less for 20 minutes. Listed checks: LEV (expansion valve), refrigerant circuit and amount. |
🟡 Book a service and quote the blink count. |
| 11 blinks per burst (outdoor recall) | The inverter cannot read its own electrical measurements. Bus-bar DC voltage cannot be detected normally (outdoor LED 8 blinks), or a compressor phase current cannot be detected (outdoor LED 9 blinks). |
🟡 Book a service and quote the blink count. |
| 14 blinks per burst (outdoor recall) | A closed service valve was detected, or the reversing (4-way) valve is not switching. Closed stop valve detected from compressor current (outdoor LED 14 blinks); 4-way valve fault detected from an abnormal indoor coil temperature (outdoor LED 16 blinks). |
🔴 Switch the system off at the isolator and call for service. |
| 16 blinks per burst (outdoor recall) | The refrigerant circuit is not behaving, a closed valve or air trapped in the system. Detected from indoor/outdoor thermistor temperatures and compressor current. Listed remedies: check for a gas leak in the connecting pipes, check the stop valve, outdoor refrigerant circuit checks. |
🔴 Switch the system off at the isolator and call for service. |
Code still showing after a reset? Mention the code and your system type when you book and our office can line up the right technician and likely parts before we arrive.
Book a service or call (02) 4760 0100 (24-hour line, Penrith & Blue Mountains).
Codes vary between models and generations, and manufacturers revise them. This guide is compiled from official service documentation and checked by Ample Air, but it is general information, not a diagnosis. Refrigerant and electrical work must be carried out by licensed technicians. Ample Air, ARC licences AU12976 & AU15788. Last verified August 2026.