This particular machine is fitted with three identical(?) normally closed (NC) solenoid valves (see pic below). The pic is of a Vetrano Evo DB courtesy of Chris' Coffee but the Lucca M58 is essentially identical. Neither the steam boiler fill solenoid nor the check valve enter into the problem area.
The is a switch with markings Tanika (tank or reservoir) and Rete (plumb-in) which tells the machine's pump where to expect the source of water. When this switch is in the Rete (plumb-in) position, the reservoir level sensor is essentially disabled and only the plumb-in solenoid is powered when the pump motor is powered. Likewise, when the switch is in the Tanika position, the reservoir level sensor is active and only the reservoir solenoid valve is powered when the pump is powered.
Since the machine operates just fine when the switch is in the Tanika (reservoir) position, this would lead me to believe that In this specific case either the switch or the plumb-in solenoid is faulty.