Daikin Altherma fault 8H-00

What it means

Outlet water after backup heater thermistor detects a too high temperature during space heating without electrical heater.

Likely causes

1. Water flow is too low
2. Faulty water pump
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. Perform a check of the water pump
3. Check refrigerant pressure sensor