Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect the inline connector in the lead to the flow sensor assembly
Disconnect LV2 connector from the PCB

Measurement:

Check the flow sensor harness leads for continuity.
Measure between the leads of the disconnected inline connector
to the red, black and yellow leads in turn at pins 4,5 and 6
respectively of the disconnected connector LV2.
Expect continuity (zero resistance).