Boiler displays F25, the burner shuts down, and this may be associated with flue issues.
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety: Turn off the power and do not operate the boiler if flue gas overheat is suspected. Flue work must be performed by a qualified engineer.
- Check flue terminal: From outside, ensure the flue outlet is clear and not obstructed by objects or vegetation.
- Ventilation: Ensure any required ventilation openings around the boiler are not blocked.
- Engineer tasks:
- Inspect the entire flue system for blockages, incorrect slope, or dislodged joints.
- Test and replace the flue gas temperature sensor if faulty.
- Check combustion settings and fan performance.
Do not attempt to dismantle or modify the flue yourself; incorrect installation is hazardous.
Repair Difficulty
Required Part
We may earn a commission from links on this page.