Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach temperature clamp to the DHW flow pipe
Ensure no DHW demand
Selector switch in CH & HW mode
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to operate for CH.
Does the DHW pipe heat up?
Notes:
Some heat may be measured initially before appliance moves diverter valve to CH position.