High
Fast flash on Worcester Bosch Greenstar 25Si

Your boiler has detected a safety-related issue with its internal heat sensors or water flow, causing it to shut down to prevent damage.

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

Five times per second. Cleared by removing fault and/or main switch off/on.

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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