High Lockout
E9224 on Worcester Bosch Greenstar Si Combi / i System

Your boiler has shut down because a safety sensor detected that the internal exhaust gases have reached a dangerously high temperature.

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 thermostat activated – flue gas thermostat overheat

What causes this fault?

This fault occurs when the boiler's internal heat exchanger becomes too hot, causing the exhaust gases to reach a temperature that could damage the unit. The most common reasons for this are a heavy buildup of limescale or debris blocking the water flow, or a failure in the internal pump that prevents heat from being moved away from the burner.

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.

Find a Gas Safe engineer
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Related fault codes

E9 219View →E2View →

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