Medium Warning
Ad on Worcester Bosch Greenstar 25HE

Your boiler is unable to communicate with its external hot water tank sensor, meaning it doesn't know the temperature of your water.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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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

Tank sensor not detected

What causes this fault?

This fault occurs when the electrical connection between your boiler's control board and the hot water cylinder sensor is broken or interrupted. The most common reason is a faulty NTC thermistor sensor that has failed internally, or a loose wiring plug that has vibrated free over time.

Engineer required

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

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Related fault codes

A7View →A8View →

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