Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Operating switch in Water position

Measurement:

Check for short circuit resistance between connections 3 (Grey) and 1 (White) on connector X3 Main Driver board.
Check for open circuit resistance between connections 3 (Grey) and 2 (Yellow) on connector X3 Main Driver board.
Turn OFF HW Tap.