High Lockout
b1 on Worcester Bosch Greenstar 25HE

Your boiler's main control chip is either loose or has failed, which means the computer can't identify the specific model to operate safely.

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

Keyed plug not detected.

What causes this fault?

This fault occurs when the small memory chip, known as a code plug, becomes loose or fails, meaning the boiler's main computer can no longer identify which model it is controlling. Without this vital identity information, the boiler shuts down immediately as a safety precaution because it doesn't know its own operating limits. The most common cause is either a vibration-related loose connection or an internal electronic failure within the plug or the main circuit 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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