BoilerFaultCodesGlow-worm 04 Fault Code
The Glow-worm 04 fault code means: your boiler has lost its electrical power supply or experienced a sudden interruption, causing it to shut down safety.. It appears on 6 Glow-worm models in our database.
Technical description: Power supply has been interrupted.
What causes the Glow-worm 04 fault?
This fault occurs when the boiler’s electronic brain suddenly loses its electrical connection, causing the unit to shut down instantly for safety. It is usually triggered by a blown internal fuse or a failure within the main circuit board that prevents power from flowing through the system. In some cases, an external issue like a tripped circuit breaker or a loose wire in the wall switch can also be the root cause.
This fault is slightly more common during stormy weather or winter months when power surges and local grid instability are more frequent.
DIY fix possible
Check if there has been a local power cut in your street or homeCheck your property's main fuse box (consumer unit) to see if a circuit breaker has trippedEnsure the boiler’s fused spur switch (usually near the boiler) is turned onTry resetting the boiler by turning the selector knob to the 'Reset' position for 5 seconds
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 04 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm 04 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