What does F2 mean on a Glow-worm boiler?
Glow-worm’s own fault-finding tables list:
- CXi and HXi ranges: F2, “Fan”.
- CI range: F2, “Fan/APS”, meaning the fan or the air pressure switch.
On the CXi range there is also a separate code, F3, “Fan unable to reach ignition speed”.
Before a boiler lights, its fan starts to push air through the burner and clear combustion gases out through the flue. The boiler confirms this is happening, either from the fan’s speed or, on older models, an air pressure switch. If it cannot confirm safe air flow, it will not light, and shows F2.
What causes an F2 fault?
- A failing fan motor. Bearings wear over the years; a fan that is noisy, slow or silent is the classic cause.
- Air pressure switch faults on models that use one, including a split or blocked sensing tube.
- A blocked or restricted flue, for example from a bird’s nest or debris at the terminal, so the fan cannot move enough air.
- Wiring or circuit board faults affecting the fan’s power or speed signal.
- Condensate backing up into the fan housing on condensing models, which can affect the fan.
What can you safely check yourself?
- Note the code and your model name from the front of the boiler.
- Listen when the boiler starts. A loud whine, a grinding noise or no fan sound at all is useful to mention in your enquiry.
- Look at the flue terminal outside from the ground only. If something is visibly blocking it, do not try to clear it yourself; mention it.
- Reset once. If F2 comes back, turn the boiler off.
When should you get an engineer?
Every time F2 returns. The fan is part of the boiler’s combustion safety, so it needs proper testing: the fan motor and speed, the air pressure switch and its tubes, the flue and the wiring. Fans and air pressure switches are replaceable, and you will be given a price before any work. On older Glow-worm boilers the engineer will also give you an honest view of whether repair is worthwhile. If the same boiler has shown F1 as well, mention that too.