BoilerFaultCodesYour boiler has shut down because the exhaust fumes have become too hot, which is a safety measure to prevent damage to the internal components.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
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 a safe limit, triggering a shutdown to protect the boiler's plastic components from melting. The most common reason is a buildup of limescale or sludge inside the main heat exchanger, which prevents heat from being transferred to the water and causes it to escape through the flue instead.
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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