F.25 High
Your boiler has shut down because it detected that the exhaust gases are getting too hot, which is a safety feature to prevent internal damage.
Technical description: Safety switch-off – flue gas temperature too high
Typical repair cost: £120-350 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Protect yourself from future repair bills
A boiler cover plan would cover faults like F.25 — no call-out fees, no surprises.
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Parts commonly replaced
- Heat exchanger (cleaning or replacement)
- Flue gas NTC sensor
- Burner seals
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