Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Turn Hot Water Tap On
CH Temperature Control set to MAX
Unclip, remove DHW microswitch and make safe
Attach pressure gauge to gas valve pressure outlet test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow burner to ignite and establish.
Within approximately 25 seconds burner pressure should increase to the CH maximum output setting.
This is factory set and can be seen on the
appliance data badge under "MAX CH".
Turn Hot Water tap OFF.
As the boiler starts to reach temperature does
the pressure modulate down?