F27
Viessmann
False flame detection / ionization fault
Flame detected when there should be none, boiler locks out for safety
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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
Shorted ionization electrode to ground, Moisture on burner or electrode, Faulty control board flame detection circuit, Incorrect grounding of boiler
How to Fix / Troubleshooting
Safety: Do not operate the boiler until the cause of false flame detection is resolved.
- Inspect ionization electrode: With power off, check that the electrode is not touching the burner or grounded metal. Clean and dry the ceramic and metal tip.
- Check for moisture: Look for condensation or leaks inside the combustion chamber. Fix any leaks and allow the area to dry completely.
- Verify grounding: Ensure the boiler is properly earthed and that there are no shared neutrals causing stray currents.
- Reset: After corrections, reset the boiler. If F27 persists, the control board may need replacement by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Ionization Electrode Assembly
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