F.28
Vaillant
Ignition Failure / No Flame Detected
Boiler displays F.28, repeated failed ignition, no flame established
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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
No gas supply or low gas pressure, Faulty ignition electrode or lead, Blocked burner or injector, Faulty gas valve or ignition control on PCB
How to Fix / Troubleshooting
Safety: If you smell gas, turn off the gas at the meter, ventilate the area, and call the gas emergency number. Do not attempt to relight.
- Check gas supply: Confirm other gas appliances (e.g. hob) work. If not, there may be a supply issue.
- Check gas cock: Ensure the boiler’s gas isolation valve is fully open.
- Reset boiler: Press the reset button once and observe. If F.28 returns after several attempts, stop resetting.
- Condensate and flue: A blocked condensate trap or frozen condensate pipe can sometimes contribute to ignition issues. Check and clear as needed (see F.75/Frozen condensate entry).
- Engineer tasks: A Gas Safe engineer will check inlet gas pressure, ignition spark, burner condition, gas valve operation, and combustion settings.
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Repair Difficulty
Professional Required
5/5
Required Part
Ignition Electrode Assembly
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