Glow-worm Boiler Fault Codes Explained
Glow-worm fault codes tell you which part of the boiler has a problem — but they don't tell you how to fix it safely. Here's what each common Betacom, Ultracom, Flexicom and Energy code means, what you can check yourself, and when to call a Gas Safe engineer.
F22 Fault
Safety switch-off — low water pressure in the boiler. Usually a simple repressurise.
F28 Fault
Ignition unsuccessful when starting up — boiler tried to light but couldn't. Often frozen condensate.
F29 Fault
Flame lost during operation — often gas pressure, flue, gas valve or fan fault.
F3 Fault
Fan unable to reach ignition speed — boiler can't confirm flue gases are being safely expelled.
When to call a Gas Safe engineer
Any work inside the boiler casing — replacing the fan, pump, igniter, flame electrode, gas valve, pressure sensor or PCB — is gas work that must be done by a Gas Safe Registered engineer. The safe checks on each fault-code page are limited to what you can do without opening the boiler.
If you can smell gas, turn off the gas at the meter, open windows, don't use switches, and call the National Gas Emergency Service on 0800 111 999 immediately.