BoilerFaultCodesGlow-worm Neon 3 NOT lit Fault Code
Also written as NEON3NOTLIT — same fault.
The Glow-worm Neon 3 NOT lit fault code means: your boiler has stopped working because it cannot confirm that the internal fan is safely clearing waste gases from the system.. It appears on 7 Glow-worm models in our database.
Technical description: Air flow proving fault - that is fan or air pressure switch.
What causes the Glow-worm Neon 3 NOT lit fault?
This fault happens when the boiler's safety system cannot detect a steady flow of air through the unit. It is usually caused by a fan that has seized over time or an air pressure switch that has failed to send the signal that waste gases are being safely removed. In some cases, bits of debris or moisture can block the small plastic tubes that monitor air flow, preventing the boiler from firing up.
This issue often surfaces during the first cold spell of autumn when a boiler that has been idle all summer is suddenly forced to work at high speeds.
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 NOT lit fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm Neon 3 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