Daikin Altherma fault U8-03

What it means

Communication abnormality between unit and room thermostat, connection NOT possible.

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 room thermistor
5. Faulty wiring between the remote controller and the unit
6. User interface (main PCB) receives no power
7. Faulty hydro PCB
8. Bad location of thermostat sensor (external influence) in case of room thermostat control (setting [C-07]=2).

Where to start

1. Check if the power supply is compliant with the regulations
2. Perform a check of the room thermistor: measure the room temperature and compare to the room temperature shown on the user interface (remote controller)
3. If temperature shown on the user interface differs from the measured temperature, replace the user interface (remote controller)