Set Appliance State:

Mains Power Off
Set Multimeter to AC Voltage Set meter to measure AC Volts
CH Demand
Summer/Winter Switch set to Winter.
Room stat at Min.
Timed/Constant Switch to Constant.
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

1. Measure voltage on pin 4.
Mains should be absent.
2.Turn room stat to Max.
There should be Mains present on pin 4.