Vaillant boiler
fault codes.
What the most common Vaillant fault codes mean, what you can safely check yourself, and when you need a Gas Safe engineer.
Before you start
- Never remove the boiler casing – only a Gas Safe engineer should work inside it
- Only reset the boiler as shown in your manual, and not more than once or twice
- If the same code keeps coming back, book a repair
Smell gas? Leave the property and call the National Gas Emergency Service on 0800 111 999.
The quick checks
- Pressure: the gauge should usually read between 1 and 1.5 bar when the boiler is cold
- Gas: do your hob and other gas appliances work? Is there credit on a prepayment meter?
- Condensate pipe: in freezing weather, is the outside plastic pipe frozen?
- Power: is the boiler’s fused spur switched on?
Common Vaillant fault codes
F.22 – Low water pressure in the heating system.
Check the pressure gauge. If it is below 1 bar, top it up with the filling loop as shown in your boiler manual, then reset. If the pressure keeps dropping, there may be a leak – book a repair.
F.28 – The boiler could not light (no flame detected when starting).
Check your other gas appliances work and your prepayment meter has credit. In freezing weather, thaw the outside condensate pipe with warm water, then reset. If it happens again, book a repair.
F.29 – The flame went out and the boiler could not relight.
The same checks as F.28: gas supply, prepayment credit and a frozen condensate pipe. Then reset. Repeated F.29 needs an engineer.
F.20 – The overheat safety cut-out has switched the boiler off.
Check the system pressure, that radiator valves are open, and for any airlocks. Reset once. If it returns, book a repair.
F.0, F.1, F.10, F.11, F.12, F.13 – A temperature sensor fault (sensor disconnected or short-circuited).
A reset may clear it for a while, but the sensor or its wiring needs an engineer.
F.23, F.24, F.72, F.83, F.84 – The boiler is reading unusual temperatures – often low water circulation, a pump, airlock or sludge problem.
Check the pressure and reset once. If it returns, book a repair. Sludge problems may need a power flush.
F.27, F.62 – A flame signal problem.
Needs an engineer.
F.32 – Fan fault.
Needs an engineer.
F.35 – The flue or air intake is blocked.
Check nothing is blocking the flue outside, then book a repair. Do not use the boiler if you suspect a flue problem.
F.53, F.54, F.57 – A combustion or gas supply problem, often shown with F.28 or F.29.
Check the gas supply and prepayment credit, and for a frozen condensate pipe, then reset. Otherwise, book a repair.
F.75 – The pressure sensor did not detect a change when the pump started.
Check the pressure is above 1 bar and top up if needed, then reset. If it returns, the pump or pressure sensor needs an engineer.
F.88 – Electrical fault with the gas valve.
Needs an engineer.
Boiler keeps breaking down?
If your boiler is old and the faults keep coming back, a replacement may cost less than you think. See fixed, fully installed prices with our online boiler price.
About this list
Codes and meanings vary between Vaillant models, so check your boiler’s manual. This guide is based on Vaillant’s published fault code information for its ecoTEC range. Vaillant’s own guide is at vaillant.co.uk.