BoilerFaultCodesGlow-worm F12 Fault Code
The Glow-worm F12 fault code means: your boiler's main control board has lost connection with the display screen, meaning the system cannot receive instructions and has stopped working.. It appears on 2 Glow-worm models in our database.
Technical description: User interface (display) communication error.
What causes the Glow-worm F12 fault?
This fault occurs when the digital conversation between the boiler's internal computer and the front display screen is interrupted. It is usually caused by a loose wiring connection or a component failure on one of the circuit boards, preventing the boiler from receiving your temperature settings.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Glow-worm models that show the F12 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F12 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