BoilerFaultCodesGlow-worm NEON5 Fault Code
The Glow-worm NEON5 fault code means: your boiler has switched itself off because it has detected that the water inside has become dangerously hot.. It appears on 7 Glow-worm models in our database.
Technical description: SAFETY TEMPERATURE LIMITER
What causes the Glow-worm NEON5 fault?
This fault occurs when the internal temperature of the boiler exceeds safe limits, triggering a safety shut-off to protect the system. The most common reason is a lack of water flow, often caused by a failing circulation pump or a blockage in the heat exchanger preventing heat from being carried away. In some cases, it can also be triggered by a faulty sensor giving an incorrect high-temperature reading.
DIY fix possible
Wait for the boiler to cool down completely (at least 20-30 minutes).Locate the reset button, typically found behind the small drop-down door or on the underside of the boiler.Press the reset button firmly; if the neon light goes out and the boiler restarts, monitor it closely.Ensure all radiator valves are open and the pump is running to prevent it happening again.
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Gas Safe Register →Glow-worm models that show the NEON5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm NEON5 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