Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach temperature clamps to the CH flow and return pipes
CH Potentiometer set to maximum
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the boiler to run up to temperature.
Measure the temperature of the flow and return pipes as close to the boiler as possible and ascertain temperature difference between flow and return.
Expected differential of approximately 20°C or lower.
Note:
To reduce the time for the test the heating load can be reduced by turning off some radiators.