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 high position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow boiler to sequence its purge period (approximately 10 seconds) measure the voltage across connection 5 (White wire) on the Main PCB connector (marked as C1) and the Neutral wire (Blue) marked N on the main connector block located on the Interconnecting Board.
Note.
Voltage only present during spark sequence.
Voltage will cease when burner fails to ignite.