Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Thermostat to Off position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure Mains Voltage across the PCB Switched Live marked SwL on connector and the Neutral marked N on the main terminal block.