Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
CH Temperature Control to MAX
Insert temperature probe to flue gas test point, ensure
it is fitted securely to prevent escape of flue gases
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow burner to ignite and establish.
Monitor flue gas temperature as appliance reaches temperature.
Does the flue gas temperature remain approx. 100°C or lower?
Note:
To reduce the time taken for this test you may wish to turn off some radiators.