BoilerFaultCodesGlow-worm Neon 2 NOT lit Fault Code
Also written as NEON2NOTLIT — same fault.
The Glow-worm Neon 2 NOT lit fault code means: your boiler has switched itself off because it has reached an unsafe temperature or a safety sensor has detected a fault.. It appears on 3 Glow-worm models in our database.
Technical description: Overheat cut off device tripped or thermostat, overheat cut off device faulty.
What causes the Glow-worm Neon 2 NOT lit fault?
This fault occurs when the water inside the boiler gets too hot, causing a safety switch to trip and shut the system down to prevent damage. The most common reasons are a pump failure that stops water from moving or a buildup of sludge and scale that blocks the flow through the heat exchanger.
This issue often surfaces during the first cold spell of autumn when the heating is turned back on after being idle all summer, which can cause the pump to seize.
DIY fix possible
Locate the overheat reset button under the boiler control panelPress the button firmly to reset the tripEnsure all radiator valves are open to allow water to circulate
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Glow-worm models that show the Neon 2 NOT lit fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm Neon 2 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 31 August 2026