Set Appliance State:

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

Observation:

Measure the temperature differential with the boiler running in central heating mode after approximately 10-15 minutes.
Expected differential 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.