F.11 High

Glow-worm F.11 Fault Code

Also written as F11 — same fault.

The Glow-worm F.11 fault code means: your boiler has detected an electrical fault with the internal sensor that monitors the temperature of the water used for your heating, causing the system to shut down for safety.. 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: Flow temperature sensor short circuit

What causes the Glow-worm F.11 fault?

This fault occurs when the boiler's internal computer receives an electrical signal suggesting the temperature sensor has malfunctioned or 'short-circuited'. The most common reason is that the sensor itself has failed internally, but it can also be caused by water leaking onto the electrical connections or a damaged wire touching the boiler's metal casing.

Typical repair cost £90-160 (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 F.11 fault code

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

Source

Glow-worm F.11 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