Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the external controls wiring or external controls link from terminals 5 and 6 of the terminal strip and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow fan purge to complete (2 minutes).
Does the boiler still try to fire for a CH demand once the fan purge has completed?