Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Insert temperature probe into flue gas test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Open hot water tap fully, allow boiler to ignite and run for demand.
Monitor flue gas temperature during operation.
Does the flue gas temperature exceed 95°C?