NEON5 High

Glow-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 11 Glow-worm models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

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.

Typical repair cost £90-220 (including labour)

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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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 7 July 2026