Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Hinge down the PCB housing
Ensure boiler is cool
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure for mains voltage between blue at 4 way mains connector and yellow wire in the middle of the 7 way connector of the PCB.
Expect 240V AC.