Boiler displays F.85, return sensor plausibility fault

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

Loose or faulty return NTC, Poor thermal contact, Wiring issues, PCB fault

Safety: Isolate power before work.

Check mounting: Ensure the return NTC is firmly clipped to the return pipe.
Test sensor: Measure resistance and compare with flow NTC at same temperature. Replace if significantly different.
Engineer diagnosis: Persistent F.85 may indicate PCB issues.

Medium 3/5

Return NTC Temperature Sensor

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