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
Gain access to PCB (use Insulation Mat as required)
Operating Switch in Heating & Water position.
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Is there approximately 90 volts across connector X3 connection 5 (L Black) and Terminal block X4 connection 2 (N Blue) on Main Driver board?