Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach temperature clamps to primary flow and return exiting the boiler as indicated
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Measure the temperature differential between the flow and return pipes from the boiler.
Initial differential may be higher but should reduce as return temperature begins to increase.
Expected differential approximately 25°c or less.
Note:
Some radiators may be turned off to reduce time taken for this test.