Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector CN9 from the PCB

Measurement:

Test 1:
Measure the resistance between pin 20 and pin 18 on connector CN9.
Test 2:
Measure the resistance between pin 19 and pin 18 on connector CN9.
Expected resistance on both tests should be approximately 8.5 kOhms or greater.
Test 3:
Measure the resistance between pin 19 and pin 20 on connector CN9 separately to a suitable earth.
Expected resistance on each test greater than 1 MOhm (O.L is greater than 1Mohm).