Set Appliance State:

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

Measurement:

Measure Mains Voltage across connection 4 (Grey wire) on PCB and N (Blue wire) on Appliance Mains Power Supply Terminal Block.