Vaillant aroTHERM fault F.729

What it means

The compressor outlet temperature is lower than 0 °C for more than 10 minutes or the compressor outlet temperature is lower than -10 °C even though the heat pump is in the operating characteristics.

Likely causes

1. Compressor outlet temperature lower than 0 °C for more than 10 minutes
2. Compressor outlet temperature lower than -10 °C even though heat pump is in operating characteristics
3. Low ambient/outdoor temperature causing heating flow temperature to drop
4. Low outdoor ambient temperature
5. Low heating flow temperature at outdoor unit
6. Heating flow temperature of outdoor unit below 4°C
7. System control failure
8. Power cut
9. Defective compressor
10. Negative outdoor temperatures Heat pump fault Power cut Defective compressor
11. Heating flow temperature below 4 °C

Where to start

1. Checking the high-pressure sensor
2. Checking that the EEV is working correctly
3. Check the condenser outlet temperature sensor (subcooling)