F3
Viessmann
Outdoor Coil Sensor Out of Range
Outdoor unit shows F3; poor heating performance on heat pump models
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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
Outdoor coil sensor drift, Sensor not properly attached, UV or weather damage to sensor cable, Faulty outdoor PCB sensor input
How to Fix / Troubleshooting
Safety: Turn off power at the outdoor isolator.
- Check mounting: Confirm the sensor is firmly attached to the outdoor coil in the original location.
- Replace sensor: If readings are clearly wrong compared to ambient conditions, install a new Viessmann-compatible NTC sensor.
- Inspect cable routing: Keep the cable away from sharp edges and hot components.
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Repair Difficulty
Medium
3/5
Required Part
Outdoor Coil Temperature Sensor (NTC)
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