Home/Boiler Fault Codes/Glow-worm F4
GLOW-WORM FAULT CODE
Glow-worm F4
An ignition fault, closely related to F1 — the flame cannot be detected. Common causes include low gas pressure, a faulty gas valve, a blocked burner, or a dirty flame sensor.
WHAT F4 TYPICALLY INDICATES
An ignition fault, closely related to F1 — the flame cannot be detected. Common causes include low gas pressure, a faulty gas valve, a blocked burner, or a dirty flame sensor.
WHAT TO DO
The boiler is not safe to keep using while displaying F4. This is not a DIY fix — it requires a Gas Safe registered engineer to diagnose and repair safely.
A NOTE ON GAS SAFE REGISTRATION
Any work on the gas side of a boiler in the UK legally requires a Gas Safe registered engineer, it isn't optional. Our engineers are fully Gas Safe registered, and you're always welcome to ask to see ID on the day. This page is general information about what a fault code typically indicates; it is not a substitute for an engineer diagnosing your specific boiler.
Seeing Glow-worm F4 on your boiler?
Tell us the code and your postcode. A fully Gas Safe registered engineer will diagnose the actual cause before quoting a fix.
Book a fault diagnosis