F.84
Vaillant
Flow Sensor / NTC Correlation Error
F.84 flow sensor plausibility fault; temperature control unstable
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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
Faulty flow sensor, Incorrectly installed flow sensor, Wiring fault between flow sensor and PCB, Faulty NTC
How to Fix / Troubleshooting
Safety: Turn off power and gas.
- Check flow sensor installation: Ensure the flow sensor is installed in the correct orientation (flow direction arrow) and fully seated.
- Inspect wiring: Check the flow sensor cable and connector for damage or loose contacts.
- Test sensor: With water flowing, verify that the sensor output changes as expected (using Vaillant diagnostic mode or multimeter as per manual). Replace if readings are erratic or absent.
- Check NTCs: Confirm that temperature sensors are reading correctly; replace any faulty NTC.
- Reset and test: After repairs, reset the appliance and verify stable temperature control.
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Repair Difficulty
Medium
3/5
Required Part
Flow Sensor Assembly
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