Daikin Altherma fault AA-01

What it means

Thermal protector is activated. Measured water temperature too high.

Likely causes

1. Water flow is too low
2. Air in the water circuit
3. Faulty refrigerant pressure sensor
4. Poor water flow through high pressure side plate heat exchanger
5. Incorrect refrigerant charge
6. Wrong setting of [F-0D] pump operation
7. Dirty water blocking the water filter
8. NOT enough air purged from the system
9. Air was purged from the water circuit after filling
10. Water pump software control behaviour based on setting [F-0D]

Where to start

1. Check the water flow
2. Check refrigerant pressure sensor
3. Check high pressure side plate type heat exchanger for good water flow and heat exchange