Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Remove plus and minus tubes from APS taking note of their positions
Note the operating pressure indicated on the pressure switch. Connect the air pressure switch charge test kit to P1 (+ve connection) on the air pressure switch
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to start the pump and fan, then increase the pressure
with the syringe to that indicated on the pressure switch, when
you reach the pressure indicated sparking should occur.
Note:
If sparking is not obtained, it is permissible
to increase the pressure by 50%
100 Pascals = 1mbar / 50 Pascals = 0.5mbar