Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connectors CN13 & CN15 from the PCB

Measurement:

Test 1.
Measure for resistance across pins 67 & 66 of connector CN13.
Expected resistance greater than 1MOhm.
Test 2.
Measure for resistance across pins 63 & 62 of connector CN15.
Expected resistance greater than 1MOhm.
Test 3:
Measure the resistance separately across pin 67 on connector CN13 & a suitable earth connection, then repeat for pin 63 on connector CN15 to earth.
Expected resistance greater than 1 MOhm for both tests.