BoilerFaultCodesGlow-worm F04 Fault Code
The Glow-worm F04 fault code means: your boiler started to light but the flame went out unexpectedly while it was running, causing the system to shut down for safety.. It appears on 1 Glow-worm model in our database.
Technical description: Ignition fault - Flame failure during operation
What causes the Glow-worm F04 fault?
This fault occurs when the boiler successfully starts but cannot maintain a steady flame, causing the system to shut down for safety. It is usually caused by a dirty or worn-out sensing probe that can no longer 'see' the fire, or a faulty gas valve that isn't providing a consistent flow of fuel. In some cases, a build-up of carbon or debris on the burner can also interfere with the combustion process.
DIY fix possible
Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is active.Check if your prepaid gas meter has credit.Reset the boiler by pressing the reset button or turning it off and on again.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Glow-worm models that show the F04 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F04 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026