Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Selector Switch ON
Gas Control Knob in Main Burner position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage across Modulation Coil connections
(Purple & Orange wires) on connector CN1.

The voltage should be greater than 16 Volts AC.