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
Remove rear cover of control panel to expose main PCB
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Mains reset switch ON.
Measure voltage across the blue and brown connections on connector marked H3 on the main PCB.
Mains voltage expected.