BoilerFaultCodesGlow-worm F.85 Fault Code
Also written as F85 — same fault.
The Glow-worm F.85 fault code means: your boiler has shut down because its internal electrical components have become too hot and need to cool down.. It appears on 6 Glow-worm models in our database.
Technical description: Electronics temperature too high
What causes the Glow-worm F.85 fault?
This fault occurs when the boiler's internal sensors detect that the main control board has reached a dangerously high temperature. It is usually caused by excessive heat building up inside the boiler casing, often due to a component failure or a loose electrical connection causing a short. To prevent permanent damage to the electronics, the system shuts down automatically to allow everything to cool over time.
This fault can be more common during heatwaves or in very small, unventilated cupboards where the ambient air temperature prevents the boiler from cooling itself effectively.
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 F.85 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F.85 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