BoilerFaultCodesGlow-worm 31 Fault Code
The Glow-worm 31 fault code means: your boiler has detected a fault with a temperature sensor and has shut down as a safety precaution, meaning you currently have no heating or hot water.. It appears on 1 Glow-worm model in our database.
Technical description: The heating flow thermistor is short circuited.
What causes the Glow-worm 31 fault?
This fault occurs when the sensor responsible for monitoring the temperature of the water leaving your boiler fails or develops an electrical short. The most common reason is that the sensor has reached the end of its life due to constant heat cycles, or moisture has compromised the electrical connection. Because the boiler can no longer accurately measure the water temperature, it shuts down to prevent the system from overheating.
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 31 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm 31 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