BoilerFaultCodesGlow-worm neon 4 not lit Fault Code
Also written as NEON4NOTLIT — same fault.
The Glow-worm neon 4 not lit fault code means: your boiler is failing to light the gas or cannot confirm that a flame is present, meaning the system has shut down for safety.. It appears on 7 Glow-worm models in our database.
Technical description: Ignition, pilot or flame proving fault
What causes the Glow-worm neon 4 not lit fault?
This fault happens when the boiler attempts to start up but cannot successfully ignite the gas or detect a steady flame. It is often caused by a blocked pilot light burner or a worn-out ignition spark, which prevents the main burner from firing up safely. In some cases, the internal control board may also fail to recognise that the flame is lit, prompting the system to shut down for your protection.
This issue often surfaces during the first cold spell of autumn when the boiler is worked harder after being mostly idle throughout the summer.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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 neon 4 not lit fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm neon 4 not lit 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