F.85 multiple flow sensor fault; appliance may not respond correctly to demand

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

Incorrect wiring of multiple flow sensors, Faulty additional flow sensor, PCB configuration error

Safety: Isolate power and gas.

Check wiring diagram: Compare actual wiring of flow sensors to Vaillant’s schematic. Correct any miswiring.
Test each sensor: Disconnect sensors one at a time and test their outputs. Replace any defective sensor.
Verify PCB configuration: Ensure the PCB is configured for the correct number and type of sensors.
Reset and test: After corrections, reset the fault and test hot water operation.

Hard 4/5

Flow Sensor Assembly

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