BoilerFaultCodesGlow-worm F08 Fault Code
The Glow-worm F08 fault code means: your boiler has detected a sensor error that prevents it from accurately measuring the temperature of the water returning from your radiators.. It appears on 1 Glow-worm model in our database.
Technical description: Central heating return NTC fault
What causes the Glow-worm F08 fault?
This fault occurs when the sensor responsible for monitoring the temperature of the water coming back from your radiators fails or provides an illogical reading. The most common reason is that the sensor's internal electrical resistance has drifted out of range, but it can also be caused by loose or corroded wiring connections following years of vibration and heat cycles.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Glow-worm models that show the F08 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F08 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