Set Appliance State:

Mains Power Off
Gas On; Pilot On
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
On/Off Switch in ON position
Mode selector switch to Constant
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure Mains voltage across connection 48 (L Red/Black) and N (Blue).