Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Gain access to lower PCB panel
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage between CH on the yellow connector (marked LR with a radiator a symbol) and mains neutral.
Mains voltage expected.
Note:
If no external controls are fitted a link should be present between L and Lr