Set Appliance State:

Mains Power Off
CH Demand
DHW Selector in Minimum (-) position
CH Selector in Maximum (+) position
ON/OFF Switch in ON position
Ensure DHW heat exchanger is cool
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow boiler to fire and run for a few minutes.
Does the DHW Heat Exchanger remain cool?