Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach pressure tube to positive connection on performance tester
Attach performance tester to gas valve outlet pressure test point
Remove the left hand side panel if required
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance if required (press reset button once then release)
Monitor the pressure registered while the fan runs and the boiler attempts to ignite.
During the sparking stage of the ignition sequence the pressure should equalise to approximately 0 mb with the fan still running.
Does the fan pressure behave as described above?
Note:
When pressure gauge is removed the pressure test point
should be tightened and checked for gas tightness.