Glow-worm boiler
fault codes.
What the most common Glow-worm 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? Only thaw it at ground level, with warm (not boiling) water
- Power: is the boiler’s fused spur switched on?
Common Glow-worm fault codes
F.22 (F9 on older models) – Low water pressure in the heating system.
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 (F1 on older models) – The boiler could not light.
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 safety cut-out has switched the boiler off (overheat).
Check the system pressure, that radiator valves are open, and for airlocks in the radiators. Reset once. If it returns, book a repair.
F.75 – The pressure did not change as expected when the pump started.
If the pressure is below 1 bar, top it up, then reset. If it returns, the pump or pressure sensor needs an engineer.
F.23, F.24, F.72, F.83, F.84 – Unusual flow and return temperatures – often low pressure, poor circulation, air in the system or a sensor problem.
Check the pressure and reset once. If it returns, book a repair. Sludge or circulation problems may need a power flush.
F.0, F.1, F.10, F.11 – 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.27 – A flame was detected while the burner was off.
Needs an engineer.
F.32 – Fan fault.
Needs an engineer.
F.61 to F.68, F.70, F.88 – A circuit board, coding or gas valve electrical fault.
Needs an engineer.
Err, or a lock code that stays after a reset – A display fault, or a safety device has locked the boiler out.
Book a repair and tell us exactly what the display shows.
Need a repair?
A diagnostic visit is £92.50 for the first 45 minutes. Once the fault is found, we give you a fixed price for the repair before any work goes ahead – often from photos or a short video of the boiler and its display.
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 Glow-worm models, so check your boiler’s manual. This guide is based on Glow-worm’s published fault code information for homeowners. Glow-worm’s own guide is at glow-worm.co.uk.