Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Disconnect connector 1 (middle) from the ignition PCB

Measurement:

Hold connector as shown in picture to ensure test is carried out on the correct pins.
Test 1:
Measure the resistance across pins 3 (blue)
and 4 (brown) on connector 1.
Resistance should be approximately 780 Ohms.
Test 2:
Measure the resistance between pin 4 (brown) wire on connector 1 and a suitable earth point.
Resistance should be at least 1M Ohm.