Daikin Altherma fault AJ-03

What it means

Triggered when the domestic hot water heat-up time exceeds 6 hours. Unit will switch to space heating/cooling for 3 hours.

Likely causes

1. Faulty backup heater
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 winding
5. Faulty hydro PCB
6. Faulty 3-way valve
7. Leaking field installed domestic hot water tap
8. Backup heater NOT allowed
9. Mismatch between the software ID and EEPROM on the PCB or user interface
10. Domestic hot water consumption too large
11. Deviation of outlet water after backup heater thermistor (lower temperature measured than actual)
12. Bad contact between sensor and pipe
13. Deviation of thermistor (lower temperature measured than actual)
14. Dirty water blocking the water filter
15. NOT enough air purged from the system
16. Water pressure NOT checked during filling
17. Air was purged from the water circuit after filling
18. Leakage
19. Expansion vessel is broken or not properly pre-adjusted
20. Deviation of thermistor (higher temperature measured than actual).
21. Backup heater wiring is NOT correct
22. User interface is replaced or reset to factory settings; previous measurements are lost
23. Hydro PCB is replaced or reset to factory settings; previous settings are lost
24. Backup heater is allowed in emergency mode, setting [4-00]
25. Special software control activated - water loop temperature is too low causing ONLY the backup heater to operate
26. Open circuit winding

Where to start

1. Perform a check of the backup heater
2. Check if the power supply is compliant with the regulations
3. Perform a check of the hydro PCB