Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Cancel purge cycle & If required, reset boiler.
Measure for A/C voltage across pins 1 & 4 of connector CN2.
Expect mains voltage.
Note:
Connector CN2 may differ in appearance but test points remain the same.