Daikin Altherma fault U8-02

What it means

Communication abnormality between unit and room thermostat after connection was already made. Unit will NOT stop operating.

Likely causes

1. Faulty or disturbance of the power supply (power supply MUST be within range of nominal operating voltage ±4%)
2. Power drop
3. Short circuit
4. Faulty wiring between the remote controller and the unit
5. Faulty room thermistor
6. User interface (main PCB) receives no power
7. Faulty hydro PCB
8. Deviation of thermistor (higher temperature measured than actual).
9. Bad contact between sensor and pipe
10. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
11. Deviation of thermistor (lower temperature measured than actual)
12. Incorrect refrigerant charge
13. Faulty expansion valve control
14. Faulty suction thermistor
15. Blockages in refrigerant circuit
16. Faulty discharge pipe thermistor
17. Domestic hot water tank thermistor measures a higher temperature than actual (component failure)

Where to start

1. Check if the power supply is compliant with the regulations
2. Check the communication wiring between the remote controller and the unit
3. Measure the room temperature and compare to the room temperature shown on the user interface (remote controller)