High Lockout
FAIL POINT K on Worcester Bosch Greenstar Si

Your boiler's main internal computer has developed a serious communication error and cannot operate, often because it has been exposed to water or has suffered an electrical failure.

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

Gas valve mode switch not set to 'NORM' or water temperature low/gas pressure issues.

What causes this fault?

This fault occurs when the boiler's main control board suffers a critical internal failure and can no longer process data to operate the system. The most common cause is water ingress from a leaking internal component dripping onto the electronics, or a power surge that has damaged the sensitive electrical tracks 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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