High Lockout
NO CODE 212 on Worcester Bosch Greenstar Si Combi / i System

Your boiler is shutting down because it is heating up much faster than it should, usually due to water not flowing through the system properly.

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

Safety or flow temperature rising too fast

What causes this fault?

This fault occurs when the water inside the boiler heats up too quickly because it isn't being moved away into your radiators or hot taps fast enough. The most common reasons are a pump that has stopped working, a blockage of sludge or limescale in the pipework, or air trapped within the system.

This issue often appears when the heating is first turned back on in autumn, as pumps can seize after being inactive throughout the summer.

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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