Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the 5 pin connector from the PCB

Measurement:

Test 1:
Measure the resistance between the 2 left hand grey wires.
Expect open circuit / O.L.
Test 2:
Run the hot water tap at 2 l/min.
Measure the resistance between the 2 left hand grey wires.
Expect continuity / zero resistance.
Is the resistance measured as expected?