F14
Viessmann
Safety High-Limit Thermostat Trip
F14 displayed, burner shuts down due to high limit trip
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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
Failed pump in hydraulic group, Blocked primary circuit, Air lock in heat exchanger, Faulty or weak high-limit thermostat
How to Fix / Troubleshooting
Safety: Turn off power and allow the unit to cool completely. Do not bypass safety thermostats.
- Reset high-limit: Locate the manual reset high-limit thermostat on the heat exchanger or flow pipe. Press the reset button if present.
- Check pump operation: When calling for heat or hot water, listen and feel for pump vibration. If the pump is not running, check its electrical connector and replace the pump motor if seized.
- Bleed air: Open air vents on the heat exchanger and nearby high points to remove trapped air.
- Inspect for blockages: Check isolation valves and strainers in the primary circuit. Ensure all valves are open and filters are clean.
- Test run: Restore power and monitor temperature rise. If the high-limit trips again quickly, further diagnosis by a technician is required to check flow rates and thermostat calibration.
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Repair Difficulty
Hard
4/5
Required Part
High-Limit Thermostat
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