Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach a pressure gauge to burner pressure test point
Remove Banjo connector from operator and connect rubber tube to connection as indicated on the image
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Blow into tube gently initially then slowly blow harder and observe the burner pressure.
When blowing down the tube does the burner pressure increase?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.