Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Boiler ON/OFF Switch OFF
CH Temperature Selector OFF
DHW Temperature Selector OFF
Remove lower front facia panel
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Boiler ON/OFF Switch ON.
Check for Mains Voltage across Terminal marked Ls and Terminal
marked Ns at connector marked ST8 on the main PCB.