F.71 displayed, flow and return temperatures appear identical or unrealistic

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

Flow and return NTCs swapped, One of the NTC sensors faulty, Wiring harness cross-connected, PCB sensor evaluation error

Safety: Isolate power before working on sensors.

Steps:

Verify that the flow NTC is installed on the flow pipe and the return NTC on the return pipe as per Vaillant diagrams.
Check that each sensor is connected to the correct PCB terminal.
Measure resistance of both NTCs and compare to specification; replace any faulty sensor.

If wiring and sensors are correct but F.71 persists, the PCB may be defective and should be replaced by a technician.

Medium 3/5

Flow NTC Temperature Sensor

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