Set Appliance State:

Set Multimeter to DC Volts Set meter to measure DC Volts
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Selector switch ON
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Test 1 :
Measure voltage on connector CN4 between pins 3 and 4 marked remote room stat.
The Voltage should be approximately 5Vdc
Test 2 :
Apply a demand and measure the voltage on connector CN4 between pins 3 and 4 marked remote stat.
The Voltage should drop to approximately 0 Vdc