Set Appliance State:

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

Observation:

Place a demand for heating and allow the boiler to heat for a few min.
Using temperature clamps for the FGA (Flue Gas Analyser) measure the temperature on the primary flow and return pipes under the boiler, there should be a differential of approx. 10-15°C between the flow and return.