Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach a tube from the + port on the telegan to the fan pressure test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the fan to run and the ignition sequence to commence.
During the ignition phase a positive pressure should be recorded.