High
F1 263 on Worcester Bosch Greenstar i

Your boiler has detected a critical failure in its internal electronic brain, meaning it has safely shut itself down and cannot operate until the hardware is repaired.

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.

What the manual says

Manufacturer manual

Control box or the HCM is defective.

From this model's manual
Verified against the Worcester Bosch Greenstar I installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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