Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Voltage Set meter to measure AC Volts
CH Demand
Gain access to PCB (use Insulation Mat as required)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across connection RI on connector block X2 and neutral (marked N) on connector block X1.
Both connector blocks are situated at the bottom L/H side of the PCB.
Note:
If no room thermostat is fitted a link will be present between "Rl" and "RL".