BoilerFaultCodesGlow-worm F11 Fault Code
The Glow-worm F11 fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water coming back from your radiators, preventing it from heating your home safely.. It appears on 15 Glow-worm models in our database.
Technical description: Return heating thermistor fault
What causes the Glow-worm F11 fault?
This fault occurs when the boiler's control board loses communication with the sensor that monitors the temperature of the water returning from your radiators. The most common reason is that the sensor has developed an internal electrical failure or the wiring connecting it to the main computer has become loose or damaged.
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 F11 fault code
Click a model for the full fault code list and model-specific repair notes.
- Betacom2 24
- Betacom2 28
- CXi Repair: £200-450
- Easicom 24 Repair: £90-160
- Flexicom 24c / 28c Repair: £120-220
- Flexicom hx Repair: £90-160
- Ultracom 2 12sxi
- Ultracom 2 18sxi
- Ultracom 2 30cxi
- Ultracom 2 30sxi
- Ultracom 2 35cxi
- Ultracom 2 SXI
- Ultracom 35 Store Repair: £100-£180
- Ultracom sxi Repair: £250-450
- Xtramax HE Repair: £250-£450
Source
Glow-worm F11 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