F.72
Vaillant
Flow/Return NTC Mismatch
Boiler shows F.72, inconsistent flow/return temperature readings
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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
One NTC sensor faulty, Sensors swapped on installation, Poor thermal contact to pipe, Wiring cross-connected
How to Fix / Troubleshooting
Safety: Isolate power and allow boiler to cool.
- Check sensor positions: Verify that the flow NTC is on the flow pipe and the return NTC on the return pipe. On some models, connectors are keyed but can still be miswired.
- Inspect clips and paste: Ensure sensors are firmly clipped to the pipes and have good thermal contact (use thermal paste if specified by Vaillant).
- Test sensors: Measure resistance of both NTCs at the same temperature; values should be similar. Replace any that are out of range.
- Correct wiring: If wiring has been disturbed, ensure each sensor is connected to the correct PCB input.
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Repair Difficulty
Medium
3/5
Required Part
Flow/Return NTC Temperature Sensors
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