BoilerFaultCodesGlow-worm F65 Fault Code
The Glow-worm F65 fault code means: your boiler's internal computer boards are having trouble communicating with each other, preventing the system from starting up.. It appears on 9 Glow-worm models in our database.
Technical description: Main PCB / Display PCB fault
What causes the Glow-worm F65 fault?
This fault occurs when the boiler's main control board loses the ability to send or receive electronic signals from the display screen panel. It is usually caused by a loose internal connection or a microscopic failure in the electrical circuits on one of the boards. Without this constant 'handshake' between components, the boiler cannot verify that the settings are safe and will stop working immediately.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Glow-worm models that show the F65 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F65 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