BoilerFaultCodesYour boiler has shut itself down because the air being pushed out of the chimney pipe has become dangerously hot.
Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now — this fault can be dangerous if ignored.
Technical description: Safety switch-off: Flue gas temperature too high
What causes this fault?
This fault occurs when the internal temperature of the exhaust gases exceeds safe limits, triggering a safety sensor to prevent damage or fire. The most common reason is a buildup of debris or limescale inside the heat exchanger, which prevents heat from being transferred to your water and instead pushes it out through the flue. It can also be caused by a faulty sensor sending incorrect readings or a lack of proper water flow through the system.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like F.25 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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