Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Operating Switch in Heating & Water position.
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Is there Mains Power present across connector CN5 connection FL (Brown) and connector CN1 N (Blue) on Ignition Control board?