Set Appliance State:

Mains Power Off
Set Multimeter to AC Voltage Set meter to measure AC Volts
CH Demand
Boiler Operating Switch / Programmer set to HEATING and WATER
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across connection 1 on connector X4 and the Neutral connection 2 (Blue wire) on connector X7 on the main PCB.
Note:
If a room thermostat is not fitted a link wire should connect connection 1 and 2 on connector X4.