Vaillant Gas boiler fault F.33
Air pressure switch fault
Gas boilerWhat it means
A fault has been detected with the air pressure switch, often linked to flue blockage or excessive counter-pressure.
Likely causes
- Air/flue pipe blocked
- Defective air pressure switch
- Cable connections not plugged in/loose
- Fan defective
- PCB defective
- Excessive counter-pressure in the air/flue pipe
Where to start
- Check the entire air/flue pipe.
- Check the cable connections.
- Check that the fan works correctly.
The full answer, free
- 2 more checks in order
- How to put it right, step by step
- The manual page for this fault (page 62), right under the answer
Safety: Isolate gas and power before you open the case. If you have been into the gas side, do a tightness test, and a combustion and flue check before you hand back. Gas Safe (UK) or RGI (Ireland) work only.
From the Vaillant manual for the Gas boiler. Check the model on the data plate before you order parts.
Other Vaillant Gas boiler fault codes
- F.00Flow temperature sensor interruption
- F.01Return temperature sensor interruption
- F.03Cylinder temperature sensor interruption
- F.10Flow temperature sensor short circuit
- F.11Return temperature sensor short circuit
- F.13Cylinder temperature sensor short circuit
- F.22Safety shutdown: water deficiency
- F.23Safety shutdown: temperature spread too great
- F.24Safety shutdown: temperature rise too fast
- F.25Safety shutdown: flue gas temperature too high
- F.27Safety shutdown: flame simulation
- F.32Fan fault
- F.64Fault: electronics/NTC
- F.65Electronics temperature fault
- F.72Flow and/or return temperature sensor fault
- F.74Water pressure sensor signal outside correct range (too high)
- F.75Pump fault/water deficiency
- F.77Accessory fault (flue non-return flap, condensate pump, etc.)
- F.83Flow and/or return temperature sensor temperature change fault
- F.84Temperature difference fault at the flow and return temperature sensors
- F.85Flow and return temperature sensors installed incorrectly (inverted)
- P.02Minimum load check programme
- S.42Flue non-return flap closed
- S.46Comfort protection: minimum load, loss of flame