Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Voltage Set meter to measure AC Volts
CH Demand
Control Thermostat in the Off position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage across connection 3 (Blue wire) on the connector marked LAMP and one of the Black wires on the connector marked LAMP N on the Interconnection Board.