Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN8 from the PCB
Disconnect the connector from the flow meter

Measurement:

Test 1.
Measure the resistance between pin 4 on connector CN8 to the grey pin on the flow meter harness.
Test 2.
Measure the resistance between pin 5 on connector CN8 to the black pin on the flow meter harness
Expect continuity / zero resistance on each test.
Also visually inspect the condition of the harness.