Daikin Altherma fault AC-00

What it means

Triggered either when no booster heater thermal protector is installed and the bridge connection over the booster heater contact is NOT made, or when a booster heater thermal protector is installed and thermal protection of the booster heater is activated due to measured water temperature being 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. If booster heater thermal protector is installed: 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