BoilerFaultCodesGlow-worm F6 Fault Code
The Glow-worm F6 fault code means: your boiler has detected a problem with the sensor that monitors the temperature of the water used to heat your radiators, causing the system to shut down for safety.. It appears on 5 Glow-worm models in our database.
Technical description: Central Heating flow thermistor fault.
What causes the Glow-worm F6 fault?
This fault occurs when the boiler's internal computer stops receiving a reliable signal from the sensor that monitors the temperature of the water leaving the unit. The most common reason is that the sensor has physically failed due to age or internal wear, though damaged wiring or loose connections between the sensor and the main control board can also be responsible.
This fault is slightly more common in winter when the boiler is working harder and the sensor is subjected to more frequent and extreme temperature cycles.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Search the official register for a qualified engineer in your area.
Gas Safe Register →Glow-worm models that show the F6 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F6 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