Vaillant aroTHERM fault F.737

What it means

Temperature in the environment circuit (cooling mode) or building circuit (heating mode) too high for compressor operation.

Likely causes

1. Temperature in the environment circuit (cooling mode) or building circuit (heating mode) too high for compressor operation
2. Feed-in of external heat into the building circuit
3. Refrigerant circuit overfilled
4. Insufficient flow rate in the building circuit
5. Temperature too high for compressor operation
6. Heating water leak
7. Loss of system pressure
8. Low or high system filling pressure
9. Leak in heating circuit
10. Air in system
11. Filling pressure outside permitted range causes flashing indication
12. Loss of heating water

Where to start

1. Check the back-up heater (heats up even though it is off in the sensor/actuator test?)
2. Check the EEV (does the EEV move to the limit stop? Use the sensor/actuator test)
3. Check the compressor outlet sensor, compressor outlet temperature sensor (TT135) and high-pressure sensor