Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to AC Voltage Set meter to measure AC Volts
Boiler mains switch On
Ensure secondary heat exchanger is cool and there is a demand for Preheat - this can be done by running the hot water with the gas turned off
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage across brown lead (live) and pink lead (neutral) at PCB side of inline connector.