Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
Gain access to PCB (use Insulation Mat as required)
Ensure NO demands
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Test 1:
Measure the DC voltage between pin 7 (red) on
connector X6 and a suitable earth point.
Expected voltage approximately 3V DC with no demand.
Test 2:
Apply a CH demand and perform Test 1 again.
Expected voltage should be approximately 0V DC with a demand.