Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach temperature clamps as indicated by the red arrows
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the burner to ignite and the boiler run with a central heating demand for 2 minutes.
Measure the temperature differential across the primary heat exchanger.
The temperature differential should be approximately 10°C or greater.
Is the temperature differential as expected?