Set Appliance State:

Mains Power Off
CH Demand
Isolate Mains Power to appliance as per TOPs P4
On/Off Switch On.
Connect a U Gauge to the Burner Gas Pressure Point at the top of the Boiler.
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the Boiler to purge itself and the Burner to ignite.
Does the Burner operate at the nominal 10.3 mb gas pressure?