Medium Lockout
F7 on Glow-worm Xtrafast 120

Your boiler has detected a problem with the temperature sensor in its hot water storage tank, which means it may struggle to heat your water correctly.

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 storage vessel thermistor fault

What causes this fault?

This fault occurs when the sensor responsible for monitoring the temperature inside the boiler's internal hot water storage tank fails or sends an incorrect signal. The most common reason is that the sensor has developed an electrical fault due to age or internal wear, meaning the boiler can no longer tell how hot the water is. Occasionally, this can also be caused by loose or damaged wiring connecting the sensor to the main control board.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

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