High Lockout
2.5 on Worcester Bosch Greenstar 25 HE Combi

Your boiler has shut down because the water in the heating system has become too hot, usually due to a lack of circulation or a blockage.

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

Max. CH flow temperature

What causes this fault?

This fault occurs when the water leaving the boiler exceeds its safe temperature limit, causing the system to shut down for safety. The most common reasons are a pump failure that prevents water from moving, or a physical blockage within the pipework or heat exchanger that traps heat inside the unit.

This issue is more frequent during the first cold spell of autumn, when central heating pumps that have been idle all summer often seize up or fail to start.

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

E9View →B7View →

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