Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector J7 (black) from the main pcb

Measurement:

Measure the resistance across the R/H red wire and R/H black wire on the disconnected connector. Open circuit should be measured.
Make safe connector J7.
Turn hot water tap On.
Measure the resistance again.
Closed circuit should be measured.