BoilerFaultCodesYour boiler has shut down because a safety sensor detected that the internal exhaust gases have reached a dangerously high temperature.
Book a Gas Safe engineer within 24–48 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like E9224 — no call-out fees, no surprises.
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