BoilerFaultCodesGlow-worm Boiler lockout indicator ON Fault Code
Also written as BOILERLOCKOUTINDICATORON — same fault.
The Glow-worm Boiler lockout indicator ON fault code means: your boiler has shut itself down for safety reasons and needs to be manually restarted to resume heating and hot water.. It appears on 2 Glow-worm models in our database.
Technical description: Safety lockout. To reset the boiler, turn the left knob on position (reset) position, wait one minute to cool down the boiler, and then turn it on previous operating position.
What causes the Glow-worm Boiler lockout indicator ON fault?
This fault occurs when the boiler's internal sensors detect an unsafe operating condition, such as the water getting too hot or the burner failing to light correctly. As a protective measure, the system 'locks out' to prevent any damage to the internal components or your property. The most common reasons include a buildup of air in the system, a blockage in the pipework, or a failure in the ignition process.
DIY fix possible
Turn the left-hand control knob to the 'Reset' positionWait for approximately one minute to allow the system to cool downTurn the knob back to your desired temperature setting
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Gas Safe Register →Glow-worm models that show the Boiler lockout indicator ON fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm Boiler lockout indicator ON 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