Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Ensure connector is refitted to Ignition Control Box
APS testing kit still attached to APS
Spark electrode lead still disconnected from its terminal and positioned it so it is resting just above its terminal as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the fan to run.
Steadily increase the pressure to that noted on the previous test.
Does sparking occur at the ignition control box?