F84 error, flow and return temperature sensors show implausible difference at start-up

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

One of the NTC sensors faulty, Sensors swapped or wired incorrectly, Poor thermal contact, PCB reading error

Safety first: Isolate power and let the unit cool.

Check sensor wiring: Ensure flow and return NTCs are connected to the correct terminals.
Compare resistances: At room temperature, both sensors should have similar resistance. Replace the one that deviates.
Improve contact: Ensure both sensors are properly clipped and in good thermal contact.
PCB diagnosis: If sensors are good and correctly wired, the PCB may be faulty.

Warning: Incorrect sensor wiring can cause unsafe temperature control.

Medium 3/5

Primary Flow NTC Sensor

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