High Lockout
E9 on Worcester Bosch Greenstar i

Your boiler has sensed that the water inside is getting too hot and has shut itself 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

Tank overheat: Tank sensor is correctly fixed to tank, Wiring and connections to sensor.

What causes this fault?

This fault occurs when the internal water temperature exceeds safe limits, forcing the boiler to shut down for safety. The most common reasons are a failed pump that isn't moving water around the system or a blockage caused by a buildup of sludge and debris in the main heat exchanger.

This issue often surfaces during the first cold snap of autumn when a pump that has been idle all summer fails to restart.

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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