Set Appliance State:

Mains Power Off
Observe the manual pressure gauge on the underside of the appliance

Observation:

Increase the system pressure slightly while observing the gauge; the gauge should respond to the increase in system pressure.
Does the pressure gauge respond to the increase in system pressure?
Note:
Ensure the system pressure is correctly set at between 1 and 1.5 bar when the appliance and system are cold.