Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Remove the screw to the right of the terminal strip and slide the tray forward to gain access to the strip its self.
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Check for mains voltage on the terminal strip of the boiler.