Medium Lockout
F.13 on Glow-worm Energy Heat

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Domestic hot water cylinder temperature sensor short circuit

What causes this 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.

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Related fault codes

F.10View →F.11View →

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