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:

Note:
You may only need to carry out one of the two following
tests if only 1 of the connectors has been wired in
(e.g. in picture only Test 1 would be required).
Test 1:
Measure voltage between CH on the yellow connector
(marked LR with a radiator symbol) and mains neutral.
Test 2:
Measure voltage between DHW on the yellow
(marked LR with a tap symbol) and mains neutral.
Mains voltage should be present on AT LEAST one of the two tests.
If no external controls are fitted a link should be present between L and Lr.