F.77 High
Your boiler has detected a blockage in the drainage pipe or an issue with the flue, preventing exhaust gases or water from leaving the system safely.
Technical description: Fault: Condensate or smoke
Typical repair cost: £100-280 (including labour)
DIY fix possible
Check the white plastic pipe leading outside (condensate pipe) to see if it is frozen during cold weather.If frozen, pour warm (not boiling) water over the external pipe or apply a heat pad to thaw it.Reset the boiler once the pipe is clear to see if the error clears.
Protect yourself from future repair bills
A boiler cover plan would cover faults like F.77 — no call-out fees, no surprises.
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Parts commonly replaced
- Condensate trap
- Condensate pump
- Internal flue seals
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