Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Integral programmer On
Selector Switch to Hot Water and Heating
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Measure voltage across the brown connection (live) at the controls terminal block and the blue (neutral) connection on the mains input terminal block.
Expect mains voltage (approx 240 VAC).