High Lockout
A7 on Worcester Bosch Greenstar Ri

Your boiler is having trouble measuring the temperature of your hot water, which usually means it cannot heat it safely or effectively.

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

Hot water sensor defective.

What causes this fault?

This fault occurs when the internal sensor responsible for monitoring the temperature of your hot water fails to send a reliable signal to the boiler's control board. The most common reason is that the sensor has physically degraded over time or developed an electrical short, meaning the boiler can no longer verify if the water is at a safe temperature. In some cases, it may also be caused by damaged or corroded wiring connecting the sensor to the main computer.

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

A8View →E9View →

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