BoilerFaultCodesGlow-worm F2 Fault Code
The Glow-worm F2 fault code means: your boiler has detected a problem with the sensor that monitors the temperature of the water leaving the unit, causing it to shut down to prevent overheating.. It appears on 7 Glow-worm models in our database.
Technical description: Heating flow thermistor fault
What causes the Glow-worm F2 fault?
This fault occurs when the internal sensor responsible for tracking the temperature of the water sent to your radiators fails or provides an illogical reading. The most common reason is that the sensor has physically degraded or developed an electrical short, meaning the boiler can no longer verify if it is operating at a safe temperature. In some cases, loose or damaged wiring between this sensor and the main control box can also trigger the error.
This fault is slightly more common in winter when the boiler is running at higher temperatures for longer periods, which places more thermal stress on the electrical components.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Glow-worm models that show the F2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F2 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