Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector J3 from the PCB
Turn hot water tap on at a flow rate of 3 l/min

Measurement:

Test 1:
Measure the resistance between pin 3 (brown) and pin 4 (black) on connector J3.
Expect open circuit.
Test 2:
Measure the resistance between pin 4 (black) and pin 5 (red) on connector J3.
Expect continuity/zero resistance.
Are the resistances measured as expected?