Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
Remove control box cover
No Demands
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

With the connector still attached to the PCB. Measure the DC voltage between the Red wire (4th down from the top) on connector X22 and the neutral at the incoming mains terminal strip.
Expect either 5vdc or 0vdc