Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach U gauge to inlet pressure test point
Ensure no other gas appliances are in operation
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the appliance to run in CH mode and the burner to ignite and establish.
Monitor the U gauge and press the mode button twice to switch the appliance central heating mode off.
(The radiator symbol will disappear from the display)
The gauge should return to standing pressure within a couple of seconds of the demand ending.
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.