Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach temperature probes to Flow and Return as indicated by the red arrows
User display control set to HW and CH
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the temperature differential with the boiler running in central heating mode after approximately 5-10 minutes.
Expected differential approximately 10-20°C.
Note:
For clarity the test is shown with the fan and burner removed but the test is carried out with these in place.
To reduce the time it takes to increase the system temperature some radiators can be turned off.