Boiler displays F84, inconsistent flow/return 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

Sensors swapped on PCB, one sensor faulty, wiring cross-connected, PCB input error

Safety: Isolate power before working on sensors.

Check connections: Verify that the flow and return NTCs are connected to the correct terminals on the PCB as per the wiring diagram.
Compare temperatures: In service mode, compare displayed flow and return temperatures; they should be plausible.
Replace suspect sensor: If one reading is clearly wrong, replace that NTC.
PCB diagnostics: If wiring and sensors are correct, the PCB may be faulty and require replacement.

Medium 3/5

Flow and Return Temperature Sensors

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