BoilerFaultCodesGlow-worm F27 Fault Code
The Glow-worm F27 fault code means: your boiler has sensed a flame when there shouldn't be one, or the sensor that monitors the fire is sending a confusing signal to the control board.. It appears on 9 Glow-worm models in our database.
Technical description: Flame detection fault
What causes the Glow-worm F27 fault?
This fault occurs when the boiler's control board detects an electrical signal suggesting a flame is present even when the gas should be turned off. The most common reason is a faulty sensing electrode that has became damp or coated in carbon, though it can also be caused by a leaking gas valve or a glitch in the main circuit board.
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 F27 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F27 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