BoilerFaultCodesGlow-worm 20 Fault Code
The Glow-worm 20 fault code means: your boiler is having trouble sending signals between its internal electrical parts, which is preventing it from working correctly.. It appears on 7 Glow-worm models in our database.
Technical description: COMMUNICATION FAULT: THIS FAULT MAY BE OCCASIONAL AND CAUSED BY ELECTROMAGNETIC INTERFERENCE, OTHERWISE CHECK THE MAIN CONTROL BOARD (PCB).
What causes the Glow-worm 20 fault?
This fault occurs when the 'brain' of the boiler loses contact with its internal electrical components, meaning it can no longer send or receive instructions. It is usually caused by a loose connection in the wiring or a hardware failure within the main control board itself. Occasionally, outside electrical interference from other household appliances can disrupt these signals and trigger the error.
DIY fix possible
Turn the boiler off at the fused spur switchWait 60 secondsTurn the power back on and press the 'Reset' button
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Gas Safe Register →Glow-worm models that show the 20 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm 20 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