Boiler shows F.84, inconsistent flow sensor readings

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 flow sensor connector, Faulty flow NTC, Wiring damage, PCB input error

Safety: Isolate power before accessing sensors.

Inspect connector: Check the flow NTC plug is fully seated and free of corrosion.
Test sensor: Measure resistance and compare with Vaillant chart. Replace if out of range.
Engineer check: If sensor and wiring are OK, PCB may require replacement.

Medium 3/5

Flow NTC Temperature Sensor

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