Set Appliance State:

Mains Power Off
Set Multimeter to AC Voltage Set meter to measure AC Volts
CH Demand
Rotary Switch in CH and DHW position
CH Operative Thermostat adjusted to Maximum
Keep Boiler Case Switch depressed
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across connector 4 (Brown wire) and connector 3 (Blue wire) on connector plug A, located on the base of the control box.