High Lockout
A8 on Worcester Bosch Greenstar Ri

Your boiler's internal computer has lost its connection with the main control board, meaning the system cannot communicate correctly to heat your home.

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

Communication interrupted.

What causes this fault?

This fault occurs when the boiler's central brain loses its ability to talk to the other internal electronic components. It is usually caused by a loose connection in the internal wiring or a component failure on the main circuit board that prevents data from flowing through the system. Think of it like a loose HDMI cable on a TV; the power is on, but the picture cannot get through.

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 →FDView →

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