Set Appliance State:

Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Isolate Mains Power to appliance as per TOPs P4
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 16V AC.