F2
Viessmann
Flame Loss During Operation
Boiler shows F2 and shuts down shortly after ignition attempt
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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 pressure, partially blocked burner, faulty gas valve, defective flame sensor circuit on control board
How to Fix / Troubleshooting
Safety warning: Flame-related faults involve combustion and gas. If you smell gas, ventilate the area, do not operate electrical switches, and call emergency gas services.
- Visual check of flue: Ensure the Viessmann concentric flue terminal is not blocked by debris, snow, or nests, which can disturb combustion.
- Check system pressure: Confirm the heating system pressure is within the recommended range (typically 1.0–1.5 bar when cold). Low water pressure can cause burner instability.
- Reset once: Use the reset button as per the user manual. If the boiler lights and then trips again with F2, stop resetting.
- Gas supply: Verify other gas appliances run steadily; if they also fluctuate, contact your gas supplier.
- Professional checks: A technician should check burner cleanliness, gas valve modulation, and flame signal using Viessmann diagnostic mode. Replace the gas valve or control board if out of spec.
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Repair Difficulty
Professional Required
5/5
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