High Lockout
A8 on Worcester Bosch Greenstar 30HE

Your boiler's internal computer has lost its connection with the main control board, preventing the system from operating.

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 to the TR 2.

What causes this fault?

This fault occurs when the boiler's internal computer modules cannot talk to each other, similar to a loose connection between a computer and its monitor. It is usually caused by moisture affecting the electrical contacts, a vibrating wiring harness that has worked loose, or a physical failure of the central control board's circuitry.

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 →C6View →

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