BoilerFaultCodesYour boiler has switched itself off because the waste gases are getting too hot, which is usually caused by a lack of water circulating through the system.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flue gas temperature too high
What causes this fault?
This fault occurs when the internal sensors detect that the exhaust gases are getting dangerously hot, triggering a safety shutdown to prevent damage. The most common reason is that heat isn't being carried away from the burner quickly enough, usually because the water isn't circulating properly or there is a blockage within the boiler's pipework.
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 F25 — no call-out fees, no surprises.
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