F36
Glow-worm
Flue Gas Recirculation / Blocked Flue
Boiler displays F36, flue gas recirculation or blockage detected
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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.
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Possible Causes
Incorrect flue terminal position, Blocked flue, Damaged flue seals, Strong wind causing recirculation
How to Fix / Troubleshooting
Safety: Turn off the boiler and do not use it until the flue system has been checked. Flue work must be done by a Gas Safe engineer.
- Visual check outside: Inspect the flue terminal for obstructions and ensure it is not too close to corners, windows, or other structures that could cause recirculation.
- Check for signs of staining: Look for soot or staining around the flue terminal, which may indicate flue gas spillage.
- Engineer tasks:
- Inspect the full flue run for blockages, dislodged joints, or incorrect slope.
- Check flue seals and gaskets.
- Verify combustion with a flue gas analyser.
Do not attempt to alter the flue position or length yourself.
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Repair Difficulty
Professional Required
5/5
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