Set Appliance State:

Mains Power Off
CH Demand
Selector switch set to CH/DHW
CH temperature control set to MAX
Preheat switched OFF
Attach temperature clamps to the flow and return pipes
underneath boiler, as close to the boiler as possible
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the boiler to run for central Heating, until noise or kettling begins.
Measure the temperature differential across flow and return.
Expected a differential of approx. 22°C or lower.
Note.
Ensure all radiators are open and system is balanced correctly
to provide correct test results.