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
Remove bottom facia panel
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across the connection RL on connector block X2 and the 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".