BoilerFaultCodesGlow-worm Neon 3 lit Fault Code
Also written as NEON3LIT — same fault.
The Glow-worm Neon 3 lit fault code means: your boiler has detected an internal electrical communication fault which is preventing it from starting up safely.. It appears on 2 Glow-worm models in our database.
Technical description: Check yellow cable between printed circuit board and air pressure switch. If satisfactory replace printed circuit board.
What causes the Glow-worm Neon 3 lit fault?
This fault occurs when the boiler's main control board loses the ability to communicate with the sensors that monitor air flow and safety. The most common reason is a failure of the internal electrical circuits on the main control board or a loose connection in the wiring that links it to the air pressure switch. Because the boiler cannot confirm it is safe to vent exhaust gases, it prevents the burner from firing as a safety precaution.
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 3 lit fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm Neon 3 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