High Lockout
A8 on Worcester Bosch Greenstar i

Your boiler's internal components are having trouble communicating with the main control board, preventing the system from starting up.

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

DHW sensor fault: DHW sensor (8000 - 20000 ohms at room temperature), Wiring and connections to sensor.

What causes this fault?

This fault occurs when the boiler's main control board loses its digital connection with internal components like the display or the heat engine sensors. It is usually caused by a loose connection in the internal wiring or a physical failure of the electronic circuit board itself, preventing the boiler from sending start-up commands. In some cases, moisture ingress or a power surge may have damaged the sensitive communication pins on the board.

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 →C6View →

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