High Lockout
AC on Worcester Bosch ZWB 7-25

Your boiler is failing to communicate with its primary control unit, meaning the system cannot start or maintain your heating and hot water.

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

Module not detected.

What causes this fault?

This fault occurs when the boiler's main control board loses the electronic 'handshake' with its internal software chip or plug-in components. It is usually caused by a loose connection during a service, a power surge that has glitched the electronics, or a component failure on the PCB itself. Essentially, the brain of the boiler can no longer see the vital parts it needs to operate safely.

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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