Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect the flow switch connector from the flow switch
Disconnect connector X2 from the PCB

Measurement:

Measure the resistance between pin 5 (white) and pin 6 (blue) wires at the disconnected plug.
Expected resistance open circuit.
Note:
Remember if a white PCB is
fitted X2 is in a different position.