BoilerFaultCodesGlow-worm F12 Fault Code
The Glow-worm F12 fault code means: your boiler’s internal control screen and main computer board have lost connection with each other, preventing the boiler from functioning.. It appears on 8 Glow-worm models in our database.
Technical description: User interface / Main PCB communication fault
What causes the Glow-worm F12 fault?
This fault occurs when the digital communication between the display panel you interact with and the boiler's internal computer breaks down. The most common reasons are a loose or corroded wiring connection between the two components, or a hardware failure on one of the circuit boards caused by age or power surges.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →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 27 April 2026