BoilerFaultCodesGlow-worm F.27 Fault Code
Also written as F27 — same fault.
The Glow-worm F.27 fault code means: your boiler has shut down because it thinks it detected a flame when there shouldn't be one, or the flame signal is being misread.. It appears on 6 Glow-worm models in our database.
Technical description: Safety switch-off – fault in flame detection
What causes the Glow-worm F.27 fault?
This fault occurs when the boiler's internal computer senses a flame signal at a time when the burner should be switched off. The most common reason is that the flame sensing component is covered in carbon deposits or the main gas valve is leaking and allowing a small amount of gas to burn when it shouldn't. In some cases, an electrical fault on the control board can cause it to 'see' a flame that isn't actually there.
This fault is more common during the winter months when the boiler is working harder, as increased usage can lead to a quicker buildup of debris on the sensing electrodes.
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 F.27 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F.27 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