Daikin Altherma fault UA-22

What it means

Communication abnormality between control box and option box.

Likely causes

1. Faulty wiring between the hydro PCB and option PCB
2. Faulty or disturbance of the power supply (power supply MUST be within range of nominal operating voltage ±4%)
3. Power drop
4. Short circuit
5. Faulty hydro PCB
6. Faulty option PCB
7. Backup heater wiring is NOT correct
8. User interface is replaced or reset to factory settings; previous measurements are lost
9. Hydro PCB is replaced or reset to factory settings; previous settings are lost
10. Backup heater is allowed in emergency mode, setting [4-00]
11. Deviation of thermistor (lower temperature measured than actual)
12. Bad contact between sensor and pipe
13. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
14. Communication error between bizone PCB and current loop PCB

Where to start

1. Check the wiring between the hydro PCB and the option PCB
2. Check if the power supply is compliant with the regulations
3. Perform a check of the hydro PCB