Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
CH Demand
CH temperature control to max
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage across terminal marked 9 and the terminal marked N on the controls installer interface.
Approximately 24 volts DC expected