Set Appliance State:

Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Isolate Mains Power to appliance as per TOPs P4
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 Mains voltage across connector X8 connection 1 (L Brown) and terminal block X7 connection 2 (N Blue)?