BoilerFaultCodesGlow-worm F.13 Fault Code
Also written as F13 — same fault.
The Glow-worm F.13 fault code means: your boiler has detected a technical fault with the sensor that monitors the temperature of your hot water tank, meaning it cannot heat your water accurately.. It appears on 6 Glow-worm models in our database.
Technical description: Domestic hot water cylinder temperature sensor short circuit
What causes the Glow-worm F.13 fault?
This fault occurs when the electrical connection to the sensor monitoring your hot water tank fails, usually due to a short circuit. The most common reason is that the sensor itself has developed an internal fault or the wiring connecting it to the boiler has become damaged or loose. Because the boiler can no longer safely tell how hot your water is, it stops heating the cylinder to prevent overheating.
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 F.13 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm F.13 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