F.29
Vaillant
Flame Loss During Operation
Boiler lights briefly then goes out, repeats several times, then shows F.29
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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
Unstable gas supply or low pressure, Blocked or partially blocked flue, Faulty ionisation electrode, Condensate backing up into combustion chamber, Fan speed/air ratio issues
How to Fix / Troubleshooting
Safety: Turn off power and gas if you suspect flue or combustion issues.
User-level checks:
- Inspect the external flue terminal for obstructions.
- Check the condensate pipe for freezing or blockage; thaw gently with warm (not boiling) water if frozen and clear any visible blockage at the trap outlet.
- Reset the boiler and observe operation.
Technician tasks:
- Check gas pressure and stability during operation.
- Inspect and clean the burner and ionisation electrode; verify correct positioning.
- Check condensate trap and siphon for blockage and clean.
- Verify fan speed and air/gas ratio using a flue gas analyser.
Persistent F.29 requires professional diagnosis to ensure safe combustion.
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Repair Difficulty
Hard
4/5
Required Part
Ionisation Electrode
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