F3 High

Glow-worm F3 Fault Code

The Glow-worm F3 fault code means: your boiler has detected that the internal mechanism responsible for clearing waste gases is not operating correctly, so it has safely shut down to prevent unsafe operation.. It appears on 6 Glow-worm models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Fan fault
Typical repair cost £180-350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Glow-worm models that show the F3 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Glow-worm F3 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 31 August 2026