Worldwide
Daikin error codes
Daikin uses two kinds of code. Wall-mounted split air conditioners flash the operation lamp, and you read a two-character code such as U4 or A5 on the remote. Altherma heat pumps show a main code and a sub code, such as 7H-01, on the indoor unit's controller. The meanings here come from Daikin's service manuals, installer reference guides and support pages.
- 24 codes
- Air conditioners & Heat pumps
- Checked against official pages
Air conditioners 12 codes
U4 Indoor and outdoor units can't communicate
The indoor unit is not receiving normal signals from the outdoor unit, so the system has stopped.
A5 Freeze-up protection or high pressure control
In cooling, the indoor coil has got so cold it could ice up, so the unit has stopped to protect itself.
U0 Refrigerant shortage
The system has worked out that not enough refrigerant is circulating, so it can't cool or heat properly and may shut down.
A6 Indoor fan motor fault
The fan inside the indoor unit is not turning at the speed the control board expects, or not turning at all, so the unit has stopped.
E7 Outdoor fan locked
The fan in the outdoor unit is not starting or turning, so the system has stopped to protect itself.
U2 Supply voltage too low or too high
The control board has seen the power supply voltage drop too low or rise too high, for example during a brief dip or power cut, and has stopped the compressor.
E5 Compressor overload protection tripped
The compressor's overload protector has tripped, so the system has stopped to protect the compressor.
E6 Compressor lock
The compressor did not start turning when the control board tried to start it, so the system has stopped.
F3 Discharge pipe too hot
The pipe carrying hot gas out of the compressor has got too hot, so the compressor has stopped to protect itself.
F6 High pressure control in cooling
While cooling, the outdoor coil has got too hot, so the unit has slowed down or stopped to keep the pressure in check.
H6 Compressor position sensor fault
The control board could not confirm that the compressor was turning properly when it tried to start it, so it has stopped.
L5 Inverter output overcurrent
The inverter that drives the compressor has seen too much current, so it has cut out to protect itself and the compressor.
Heat pumps 12 codes
7H-01 Water flow problem
Not enough water is flowing round the heating circuit, so the heat pump has stopped for the moment.
89-01 Heat exchanger frozen
The heat pump's freeze protection has been triggered several times in a short period, so it has shut down to protect the water heat exchanger from freezing.
U4-00 Indoor and outdoor units not communicating
The indoor unit can't communicate with the outdoor unit, so the heat pump can't run.
AA-01 Backup heater overheated
The electric backup heater in the indoor unit got too hot and its safety cut-out has tripped, so the heat pump has stopped.
AH-00 Tank disinfection not completed
The regular hot water tank disinfection cycle didn't reach or hold its target temperature.
AJ-03 Hot water taking too long to heat up
Heating the hot water tank has taken too long, so the heat pump has switched to space heating for a while.
80-00 Return water temperature sensor fault
The sensor that measures the water coming back from your radiators or underfloor heating is giving a reading the heat pump can't use, so it has stopped.
81-00 Flow water temperature sensor fault
The sensor that measures the water leaving the heat pump for your radiators or underfloor heating is giving a reading the heat pump can't use, so it has stopped.
U0-00 Refrigerant shortage
The outdoor unit has detected a shortage of refrigerant in the sealed refrigerant circuit.
E7-00 Outdoor unit fan motor fault
The fan in the outdoor unit isn't starting or running properly, so the heat pump has stopped.
E1-00 Outdoor unit circuit board fault
The main circuit board in the outdoor unit has found a problem with its memory (EEPROM), so the heat pump has stopped.
A1-00 Mains power signal problem (zero cross)
The outdoor unit's board isn't reading the mains supply properly, so the heat pump has stopped.
No codes of that type for this brand.
Good to know
- Air conditioners: To read the code, point the remote at the indoor unit and hold the timer cancel button for about 5 seconds until 00 flashes in the temperature display. Keep pressing the same button: a short beep or two beeps means it is not that code, a long continuous beep means the code on screen is the fault. Hold the button for 5 seconds to finish, or leave the remote alone for a minute.
- Air conditioners: Some Daikin remotes, such as the ARC447A, show the code straight after the 5-second hold. Some remotes in the ARC433B range use a different check with the TEMP and MODE buttons, which Daikin describes in its service documents.
- Air conditioners: Daikin's troubleshooting page says that if the operation lamp flashes, switch off the air conditioner's own circuit breaker (not the main switch for the whole house), wait 20 minutes, then switch it back on. If the lamp flashes again, Daikin says the unit is likely to be faulty.
- Altherma heat pumps: Daikin's installer reference guide says the cause of an error should be understood and put right before the code is reset, and that this should be done by a licensed installer or your local dealer. The controller shows how to reset each code.
- Altherma heat pumps: Some codes clear themselves: Daikin says 7H-01 resets automatically after some time, AJ-03 resets once the tank heats up normally, and AH clears once a disinfection cycle completes.
- Altherma heat pumps: If the heat pump fails, Daikin's user reference guide explains that the backup heater can take over the heating, either automatically or after you confirm it on the Malfunctioning screen. Electricity use will be considerably higher.
Official help pages
- Daikin: Simple Self-Diagnosis by Malfunction Code, SM-TS3, list of error codes (PDF)
- Daikin: How to check error codes, SM-TS3 pages 7 to 8 (PDF)
- Daikin Altherma 3 R W installer reference guide 4P496758-1B (ERGA-D, EHBH/EHBX-D), troubleshooting and error codes, p. 89 (ManualsLib copy)
- Daikin Altherma 3 R W installer reference guide 4P496758-1B, error codes, p. 90 (ManualsLib copy)
Every code page links the exact pages it was checked against. Last reviewed October 2026.
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344 codes from 24 brands, each one checked against the maker's own manuals and support pages.