Vaillant aroTHERM fault F.731

What it means

Refrigerant pressure too high; the integrated high-pressure switch in the outdoor unit has tripped at 41.5 bar (g) or 42.5 bar (abs).

Likely causes

1. Refrigerant pressure too high
2. Insufficient energy output via the condenser
3. Purging the building circuit
4. Too low a volume flow as a result of closing single room controls in an underfloor heating system
5. Refrigerant flow rate too low (e.g. electronic expansion valve defective, 4-port diverter valve is mechanically blocked, filter is blocked)
6. Air in building circuit
7. Dirt filter blocked
8. Fan unit dirty (cooling mode)

Where to start

1. Check that the dirt filter that is in place is permeable
2. Cooling mode: Check the fan unit for dirt
3. Check the high-pressure switch and high-pressure sensor