F27
Saunier Duval
Flame Detection Error (False Flame Signal)
Furnace displays F27, ignition is blocked, may occur immediately on power-up
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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
Moisture or contamination on ionization electrode,Faulty ionization cable,PCB detecting flame when none is present,Incorrect earthing or reversed polarity
How to Fix / Troubleshooting
Safety first: Isolate power and gas. Only qualified personnel should access combustion components.
- Check mains polarity and earth: Have an electrician verify correct live/neutral orientation and a solid earth connection to the appliance.
- Clean ionization electrode: Remove and clean the electrode tip. Ensure it is dry and free from soot or corrosion.
- Inspect cable: Replace the ionization cable if the insulation is cracked or if there are signs of tracking.
- PCB test: If false flame is still detected with the electrode disconnected (tested by a technician), the PCB flame detection circuit is likely faulty and the board must be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Ionization Electrode
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