Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Selector Switch to Hot Water and Heating
Turn CH thermostat up to MAX
Attach Performance Tester Temperature Clamps
on flow and return pipes as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler and system to heat.
Measure the difference in temperature between the flow and return pipes.
Is the differential approx. 20°C or lower?
Note:
Differential may be higher on initial start-up, allow boiler to run until return pipe starts to heat or the boiler shuts down before selecting an option. Turning off some radiators may reduce time taken for this test.