F10 High

Glow-worm F10 Fault Code

The Glow-worm F10 fault code means: your boiler has detected that its temperature sensors are incorrectly placed or wired, preventing it from calculating how much heat is being delivered to your home.. It appears on 14 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: Central heating return thermistor fault

What causes the Glow-worm F10 fault?

This fault occurs when the boiler's control board detects that the temperature readings from the internal pipework are coming back in the wrong order. The most common reason is that the flow and return sensors have been physically clipped onto the wrong pipes or the wiring connectors have been swapped during a previous repair. Because the boiler cannot accurately monitor how heat is moving through the system, it shuts down as a safety precaution.

Typical repair cost £90-180 (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 F10 fault code

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

Source

Glow-worm F10 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 7 July 2026