The water level is maintained by an autofill circuit.
In the majority of La Cimbali models this is a probe which goes down into the tank and detects the water level.
Firstly this probe requires the passage of current to work. If you are using demineralised / deionised / distilled or reverse osmosis water - there are no ions in the water for conduction - no current flow and the water wont be detected.
If using softened water that will be fine. Now the probe can get coated with a layer of scale which will also insulate it..... no water detection.
If the lead at the end of the probe has come off or is loose again no current flow.
The detection circuit is a relay. If that is faulty it can cause autofill to operate when it shouldnt.
The autofill operates a solenoid (and the pump).... but if the solenoid is faulty (on a plumbed in unit) then water from the mains can pass into the boiler.....
If it is a fully automatic (volumetric) model autofill is managed by the computer board rather than just a relay.... and these boards can develop faults.....
Whatever the cause, it needs to be found and corrected before attempting to use the machine or water will shower out from the overpressure valve over all the internals..... and if this gets onto the ends of the heater for example it can cause damage by wicking up into the heater element (and also short out other electrical bits)....
Best of luck - they are a great machine once working correctly.