F14
Viessmann
Gas valve control / modulation fault
Gas valve error, boiler does not fire, control indicates gas valve or modulation fault
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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
Defective modulating gas valve, Loose gas valve wiring harness, Incorrect gas type setting on control, Faulty control board output to gas valve
How to Fix / Troubleshooting
Safety: Gas components must only be serviced by licensed gas technicians. Do not attempt to open or adjust the gas valve.
- Check external gas supply: Confirm that the main gas cock to the boiler is open and that other gas appliances function.
- Visual wiring check: With power off, inspect the gas valve connector on the Viessmann gas valve. Ensure it is fully seated and the harness is not damaged.
- Reset control: Restore power and reset the boiler once. If F14 reappears, do not continue to reset.
- Professional diagnosis: A technician will measure gas valve coil resistance, verify correct gas type configuration in the Viessmann service menu, and replace the gas valve or control board if necessary.
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Repair Difficulty
Professional Required
5/5
Required Part
Modulating Gas Valve
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