High Lockout
A8 on Worcester Bosch Greenstar 25HE

Your boiler's internal computer has lost contact with its control panel or external sensors, meaning it cannot receive the instructions it needs to work.

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

Break in communication

What causes this fault?

This fault occurs when the boiler's main control board can no longer 'talk' to the display screen or external controls. The most common reason is a loose connection in the internal wiring, though it can also be caused by moisture damage or a component failure on one of the electronic circuit boards.

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

A7View →B1View →E9View →

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