Viessmann Indoor Coil Sensor Out of Range

Indoor unit shows F2; coil temperature reading appears abnormal in diagnostics

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.

Possible Causes

Sensor not in good thermal contact with coil, Sensor damaged by corrosion or cleaning chemicals, Wiring harness partially broken, Indoor PCB sensor input fault

How to Fix / Troubleshooting

Safety: Isolate power before working on the coil area.

Re-seat sensor: Ensure the sensor is tightly clipped to the coil tube or fin with good contact.
Inspect for corrosion: Replace the sensor if the casing is cracked or corroded.
Check harness continuity: Wiggle the cable gently while measuring resistance to detect intermittent breaks.

If F2 persists with a new sensor and good wiring, the indoor PCB likely needs replacement.

Repair Difficulty

Medium 3/5

Required Part

Evaporator Temperature Sensor (NTC)

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