F16
Viessmann
DHW sensor fault
Domestic hot water (DHW) temperature sensor error on combi or indirect systems
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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 DHW NTC sensor in cylinder or plate heat exchanger, Loose sensor pocket contact, Damaged sensor wiring, Incorrect sensor type installed
How to Fix / Troubleshooting
Safety: Isolate power and allow hot water components to cool before handling.
- Locate DHW sensor: On Viessmann systems with a cylinder, the DHW sensor is inserted into a sensor well on the tank. On combi units, it may be clipped to the DHW outlet or plate heat exchanger.
- Check seating: Ensure the sensor is fully inserted into the pocket and secured. Poor contact can cause incorrect readings.
- Inspect cable: Follow the cable back to the control board and check for damage or loose connectors.
- Reset and test: Restore power and reset the boiler. Run hot water and monitor operation. If F16 returns, the sensor likely needs replacement.
- Use correct part: Replace only with a Viessmann-specified NTC sensor to ensure compatibility.
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Repair Difficulty
Medium
3/5
Required Part
DHW Temperature Sensor (NTC)
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