F7
Viessmann
Return Temperature Sensor Fault
Boiler displays F7, may overheat quickly or not fire at all
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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 return NTC sensor, wiring short to flow sensor, incorrect sensor placement, PCB input fault
How to Fix / Troubleshooting
Safety: Overheating can damage the heat exchanger. Do not run the boiler repeatedly with this fault.
- Visual inspection: Locate the Viessmann return NTC on the return pipe. Check for secure mounting and correct contact with the pipe.
- Compare temperatures: If the boiler has a service menu, compare displayed flow and return temperatures. A large unrealistic difference suggests a sensor fault.
- Check wiring: Ensure the return NTC cable is not swapped with the flow NTC on the PCB.
- Replace sensor: If in doubt, replace the return NTC with a genuine Viessmann part.
- Persistent F7: Requires PCB diagnostics and possible replacement by a service technician.
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Repair Difficulty
Medium
3/5
Required Part
Return Temperature Sensor (NTC)
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