Daikin Altherma Heat Pump Error Codes

Complete diagnostic guide for Daikin Altherma heat pumps in the United Kingdom.

System and Communication Errors

Error codes for Daikin Altherma heat pumps related to system errors and communication problems.

Error Code	Meaning	Possible Causes	Solutions
UA	Incorrect combination of indoor and outdoor unit	Incompatible combination of indoor and outdoor unit Incorrect model combination Configuration error	Check combination of indoor and outdoor unit Check model compatibility Check configuration Contact qualified service if necessary
U0	Refrigerant shortage	Refrigerant leakage Insufficient refrigerant amount Problems with refrigerant circuit	Have refrigerant circuit checked for leaks Check refrigerant amount (only by qualified service) Have refrigerant refilled if necessary Contact qualified service
U2	Voltage drop or overvoltage in main circuit	Voltage drop in main circuit Overvoltage in main circuit Problems with power supply Electrical connection problems	Check power supply Check voltage in main circuit Check electrical connections Contact electrician if necessary
U4	Communication error between indoor and outdoor unit	Communication error between indoor and outdoor unit Wiring damaged Defective control board Problems with data transmission	Check wiring between indoor and outdoor unit Check control board for errors Check communication connections Restart system Contact qualified service if problem persists

Indoor Unit Errors

Error codes for Daikin Altherma heat pumps related to indoor unit problems.

Error Code	Meaning	Possible Causes	Solutions
A1	Indoor board (PCB) defect	Indoor board defective Hardware error on board Electronic components damaged	Check indoor board for visible damage Restart system Have indoor board checked by qualified service Have board replaced if defective Contact qualified service for diagnosis
A5	Frost protection activated	Frozen heat exchanger Insufficient water flow Low ambient temperature Problems with heat dissipation	Check heat exchanger for freezing Increase water flow Check ambient temperature Check heat dissipation Allow system to defrost Contact qualified service if problem persists
A6	Indoor unit fan motor error	Fan motor defective Fan blocked Fan wiring damaged Problems with fan control	Check fan for blockages Test fan motor for function Check wiring Replace fan motor if defective Contact qualified service
C4	Heat exchanger temperature sensor error	Heat exchanger temperature sensor defective Sensor not properly connected Cable connection interrupted Sensor damaged	Check heat exchanger temperature sensor for function Check wiring for proper connection Test sensor with multimeter Replace sensor if defective Contact qualified service
C9	Intake air temperature sensor error	Intake air temperature sensor defective Sensor not properly connected Cable connection interrupted Sensor damaged	Check intake air temperature sensor for function Check wiring for proper connection Test sensor with multimeter Replace sensor if defective Contact qualified service

Outdoor Unit - Compressor and Motor Errors

Error codes for Daikin Altherma heat pumps related to compressor and motor problems in the outdoor unit.

Error Code	Meaning	Possible Causes	Solutions
E1	Outdoor unit circuit board (PCB) error	Outdoor board defective Hardware error on board Electronic components damaged	Check outdoor board for visible damage Restart system Have outdoor board checked by qualified service Have board replaced if defective Contact qualified service for diagnosis
E5	Inverter compressor motor overheating	Compressor motor overheated Insufficient cooling Problems with compressor High load	Allow system to cool down Check cooling system Check compressor for function Reduce load Contact qualified service if problem persists
E6	Compressor start error	Compressor does not start Start problems Compressor defective Electrical problems	Check compressor for function Check electrical connections Restart system Have compressor replaced if necessary Contact qualified service
E7	Outdoor unit fan motor error	Fan motor defective Fan blocked Fan wiring damaged Problems with fan control	Check fan for blockages Test fan motor for function Check wiring Replace fan motor if defective Contact qualified service
E8	Input overcurrent	Overcurrent in input circuit Electrical problems Problems with power supply	Check power supply Check input current Check electrical connections Contact electrician if necessary

Outdoor Unit - Sensor and Temperature Errors

Error codes for Daikin Altherma heat pumps related to sensor and temperature problems in the outdoor unit.

Error Code	Meaning	Possible Causes	Solutions
H0	Sensor error	Various sensors in system defective Sensor not properly connected Cable connection interrupted Sensor damaged	Check all sensors in system Check wiring for proper connection Test sensors with multimeter Replace sensor if defective Contact qualified service
H6	Operation stopped due to faulty position detection sensor	Position detection sensor defective Sensor not properly connected Cable connection interrupted	Check position detection sensor for function Check wiring Replace sensor if defective Contact qualified service
H8	DC current sensor error	DC current sensor defective Sensor not properly connected Cable connection interrupted	Check DC current sensor for function Check wiring Replace sensor if defective Contact qualified service
H9	Intake air temperature sensor error	Intake air temperature sensor defective Sensor not properly connected Cable connection interrupted Sensor damaged	Check intake air temperature sensor for function Check wiring for proper connection Test sensor with multimeter Replace sensor if defective Contact qualified service
J3	Discharge pipe temperature sensor error	Discharge pipe temperature sensor defective Sensor not properly connected Cable connection interrupted Sensor damaged	Check discharge pipe temperature sensor for function Check wiring for proper connection Test sensor with multimeter Replace sensor if defective Contact qualified service
J6	Heat exchanger temperature sensor error	Heat exchanger temperature sensor defective Sensor not properly connected Cable connection interrupted Sensor damaged	Check heat exchanger temperature sensor for function Check wiring for proper connection Test sensor with multimeter Replace sensor if defective Contact qualified service
P4	Inverter circuit heatsink temperature sensor error	Heatsink temperature sensor defective Sensor not properly connected Cable connection interrupted Sensor damaged	Check heatsink temperature sensor for function Check wiring for proper connection Test sensor with multimeter Replace sensor if defective Contact qualified service

Outdoor Unit - Pressure and Overheating Errors

Error codes for Daikin Altherma heat pumps related to pressure and overheating problems in the outdoor unit.

Error Code	Meaning	Possible Causes	Solutions
F3	High discharge pipe temperature / Compressor overheating	High temperature at discharge pipe Compressor overheated Insufficient cooling Problems with refrigerant circuit	Allow system to cool down Check compressor for overheating Check cooling system Check refrigerant circuit Contact qualified service if problem persists
F6	High pressure protection in cooling mode	High pressure in cooling mode Blocked heat exchanger Insufficient airflow Problems with refrigerant circuit	Check heat exchanger for blockages Increase airflow Check refrigerant circuit Monitor pressure Contact qualified service if necessary
L3	Electrical component overheating	Electrical components overheated Insufficient cooling High load	Allow system to cool down Check cooling system Reduce load Check electrical components Contact qualified service if problem persists
L4	High temperature at inverter circuit heatsink	Inverter circuit heatsink overheated Insufficient cooling Problems with inverter	Allow system to cool down Check inverter circuit heatsink Check cooling system Check inverter for function Contact qualified service if problem persists
L5	Output overcurrent	Overcurrent in output circuit Electrical problems Problems with inverter	Check output current Check electrical connections Check inverter for function Contact electrician if necessary

Need More Help?

If you are experiencing problems with your Daikin Altherma heat pump that are not covered by these error codes, or if the provided solutions do not resolve your issue, we recommend:

Consult your Daikin Altherma heat pump installation manual for model-specific information
Visit the official Daikin support page: daikin.com/uk/en/support.html
Contact an authorized Daikin service partner in the United Kingdom
Seek help from a qualified heat pump repair technician
Check warranty coverage if your heat pump is still under warranty

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