High Lockout
F.12 on Glow-worm Energy System

Your boiler has lost its ability to monitor the temperature of your hot water cylinder because a sensor has developed an electrical fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Cylinder temperature sensor short circuit

What causes this fault?

This fault occurs when the electrical monitoring system detects a short circuit in the sensor that measures the heat of your hot water tank. The most common reason is that the internal components of the sensor have failed, or the wiring connecting it to the boiler has become damaged or pinched. As a result, the boiler can no longer safely determine if the water is at the correct temperature and will stop heating the cylinder as a safety precaution.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.11View →

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