Daikin air conditioning systems use a comprehensive fault code system to communicate system status and fault conditions. Here is a guide to the most common Daikin error codes we see across our repair call-outs in Surrey, Sussex and South London, what they mean and what to do about them.
How Daikin Displays Error Codes
Daikin indoor units typically display error codes on the unit’s LED display or through indicator light flash sequences. The Daikin Intelligent Eye function (where fitted) can sometimes clear minor faults automatically. For units with a wired controller, the code displays directly. For units with a wireless remote only, some models require pressing a specific button combination to view the stored fault code — refer to your installation manual for the specific procedure for your model.
A-Series — Communication and Control Faults
A1: Indoor unit PCB fault. The main circuit board of the indoor unit has detected a fault. Causes range from power supply issues to component failure on the board. Requires engineer investigation — PCB testing and potentially replacement.
A3: Drain level sensor fault or float switch operation. The condensate drain pan has reached the overflow level or the float switch has operated. Check the condensate drain pipe for blockages. This is one of the most common fault codes we attend — a small algae blockage in the drain pipe is usually the cause and resolves quickly with drain cleaning.
A5: Freeze-up protection. The indoor unit has shut down to prevent the evaporator coil from freezing. Check and clean the air filter. Allow any ice present to defrost (typically 30-60 minutes) before restarting. If the fault recurs after filter cleaning, low refrigerant or fan fault may be the underlying cause.
A6: Fan motor fault on the indoor unit. The indoor fan motor has failed or is running outside specification. Requires engineer attendance for motor testing and replacement if necessary.
A7: Swing flap motor fault. The motorised horizontal airflow flap has failed. The system may continue to operate but the flap will not move. Flap motor replacement is a relatively minor repair.
C-Series — Sensor Faults
C4: Indoor unit heat exchanger (evaporator) temperature sensor fault. The thermistor measuring refrigerant temperature in the indoor unit has failed. Requires replacement — typically a straightforward repair with good parts availability for Daikin units.
C5: Indoor unit inter-connector wiring fault. Communication wiring between indoor unit components has an issue. Check connections. May indicate PCB fault.
C9: Indoor unit suction air temperature sensor fault. Similar to C4 — thermistor replacement required.
E-Series — System Faults
E1: Outdoor unit PCB fault. The control board of the outdoor unit has detected a fault. Requires engineer investigation. Can indicate a range of underlying issues from power supply problems to component failure.
E3: Outdoor unit high pressure fault. The refrigerant pressure on the high pressure side has exceeded safe limits. Common causes: dirty or blocked condenser coil on the outdoor unit (clear debris from around the unit), high ambient temperature, or a failing expansion valve. Do not continue to operate the system with this fault. Call an engineer.
E4: Outdoor unit low pressure fault. Refrigerant pressure on the low pressure side is below the minimum threshold. The most common cause is a refrigerant leak — the system has lost refrigerant charge. The system will not cool effectively and may cause compressor damage if run in this condition. Switch off and call an engineer. Refrigerant top-up without leak repair is not a solution — the leak must be found and fixed first.
E5: Outdoor unit motor overcurrent. The outdoor fan motor is drawing excessive current. May indicate a failed motor bearing, debris in the fan, or a PCB fault. Switch off and call an engineer.
E7: Outdoor unit fan motor fault. Similar to E5. Outdoor fan motor testing and potentially replacement required.
E9: Electronic expansion valve fault. The expansion valve controls refrigerant flow through the system. A fault here causes incorrect refrigerant distribution, leading to poor cooling and potentially compressor damage. Requires engineer diagnosis and valve replacement if confirmed.
F-Series — Refrigerant Faults
F3: Discharge pipe temperature too high. The compressor discharge temperature has exceeded limits — typically caused by low refrigerant charge, high ambient temperature or a failing compressor. Switch off immediately and call an engineer.
F6: Refrigerant overcharge. The system contains too much refrigerant — typically only occurs after an incorrect service or installation. Requires refrigerant recovery and recharge to correct level by an F-Gas certified engineer.
H-Series — Compressor Faults
H3: High pressure switch fault. The high pressure safety switch has operated or has failed. Do not restart the system — call an engineer. High pressure faults can indicate serious system problems.
H6: Position sensor fault on DC fan motor. Requires engineer investigation.
H7: DC fan motor position sensor fault (outdoor unit). Fan motor or PCB issue requiring engineer attendance.
H9: Outdoor air temperature sensor fault. The thermistor measuring outdoor ambient temperature has failed. The system may still operate but efficiency optimisation will be affected. Sensor replacement required.
Getting Daikin Repairs Done
Daikin has excellent UK parts availability — one of the benefits of being the world’s largest air conditioning manufacturer. We carry common Daikin parts and can source others typically within 24-48 hours. For most fault codes we achieve first-time fix. Call 07833 053749 or contact us online.