BoilerFaultCodesGlow-worm Reset Light / Overheat Fault Code
Also written as RESETLIGHTOVERHEAT — same fault.
The Glow-worm Reset Light / Overheat fault code means: your boiler has switched itself off because it has reached an unsafe temperature, usually caused by a circulation issue or a temporary blockage.. It appears on 4 Glow-worm models in our database.
Technical description: If the overheat Safety Temperature Limiter operates as indicated by illuminated reset light, open the controls cover and turn temperature control to “0” (anticlockwise) and then back to original position
What causes the Glow-worm Reset Light / Overheat fault?
This fault occurs when the water inside the boiler exceeds a safe temperature limit, triggering a safety shut-off to protect the internal components. The most common reasons are a failing circulation pump that isn't moving water through the system fast enough or a buildup of debris that has partially blocked 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 internal parts like the pump to seize.
DIY fix possible
Open the control cover on the front of the boilerTurn the temperature control knob fully anticlockwise to the '0' positionWait a few seconds, then turn the knob back to your original desired temperature setting to restart the boiler
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Gas Safe Register →Glow-worm models that show the Reset Light / Overheat fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm Reset Light / Overheat 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