Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Boiler On/Off Switch ON
CH Switch OFF
DHW Switch in INSTANT position
Connect a U-gauge to the burner pressure test point
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Does the U-gauge indicate approximately 10.6mb gas pressure and does burner fail to light correctly?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.