BoilerFaultCodesYour boiler has switched itself off because it has detected that the exhaust gases have become too hot, which is a safety protection measure.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flue overheat thermostat may have operated. Press the reset button on the flue overheat thermostat.
What causes this fault?
This fault occurs when the internal temperature of the exhaust gases reaches a level that could damage the boiler's components or the flue system. The most common reasons for this are a build-up of limescale or sludge inside the main heat exchanger, which prevents heat from transferring to the water, or a fault with the fan and air pressure system. Because the heat has nowhere to go, it builds up until a safety sensor triggers an immediate shutdown.
This fault is more common during the winter months when the boiler is running at maximum capacity for long periods to meet higher heating demands.
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 Section M (Neon Flashing) — no call-out fees, no surprises.
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