F27
Protherm
Flame Detection Error / False Flame Signal
Boiler shows F27, ignition attempts fail or flame is detected at the wrong time
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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 ionisation electrode, Faulty flame sensor or cable, Incorrect earth or polarity of mains supply, PCB flame detection circuit fault
How to Fix / Troubleshooting
Safety: Isolate power and gas. Work inside the combustion chamber must be done by qualified personnel.
Steps:
- Inspect the ionisation electrode for cracks, soot, or moisture. Clean and dry thoroughly, or replace if damaged.
- Check the ionisation cable for insulation damage and secure routing away from high‑voltage leads.
- Verify correct earthing and polarity at the boiler’s mains connection. Correct any wiring errors.
- If false flame is still detected, the PCB may be faulty and require replacement.
After repair: Test multiple ignition cycles to ensure stable flame detection and no F27 errors.
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Repair Difficulty
Hard
4/5
Required Part
Ionisation Electrode
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