BoilerFaultCodesGlow-worm F01 Fault Code
The Glow-worm F01 fault code means: your boiler has stopped working because a sensor that monitors the temperature of the water returning from your radiators has developed a fault.. It appears on 9 Glow-worm models in our database.
Technical description: Return heating thermistor fault
What causes the Glow-worm F01 fault?
This fault occurs when the boiler's control board receives an incorrect or missing electrical signal from the sensor that monitors water temperature coming back from your radiators. The most common reason is that the sensor has physically failed due to age, though it can also be caused by loose or damaged internal wiring.
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 F01 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F01 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
- Glow-worm Betacom2 28 manual (PDF)
- Glow-worm Easicom 28 manual (PDF)
- Glow-worm Ultracom 2 35cxi manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026