F14
Viessmann
Mains Voltage / Power Supply Fault
Boiler shows F14, burner does not start, display may show low voltage warning
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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
Low or unstable mains voltage, incorrect phase/neutral connection, internal power supply fault on PCB, loose terminal connections
How to Fix / Troubleshooting
Safety: Electrical work must comply with local regulations. Isolate power before opening the boiler.
- Check supply: Verify the boiler is connected to a dedicated fused spur with correct polarity and earth.
- Measure voltage (technician): A professional should measure mains voltage at the boiler terminals; values significantly below nominal can trigger F14.
- Inspect terminals: Tighten any loose live, neutral, or earth connections inside the boiler's electrical box.
- Surge protection: If the property experiences frequent surges, consider installing surge protection to protect the PCB.
- PCB replacement: If mains supply is stable but F14 persists, the internal power supply on the control board may be defective and require replacement.
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Repair Difficulty
Hard
4/5
Required Part
Main Control Board
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