I'm thinking the Boiler Fill Solenoid is not working correctly but I'm not sure...
That is correct - the boiler fill solenoid valve
IS NOT opening. Do not operate the machine until problem is resolved as you
may be very low on water in the boiler.
Syphon as much water out of the boiler as you can. Remove the hot water tube (item 2) by loosening & removing fittings 1 & 3. An adaptor fitting will remain in the boiler. Fit a hardware store plastic tube over the exposed threads and syphon away. Then fit a smaller plastic tube inside the fitting and syphon the remaining water out.

Remove the top half of the solenoid valve and soak in white vinegar for 30 minutes:

Have some paper towels handy as you will get a little leakage from what you could not syphon out. After the 30 minute soak, reassemble and you should be "good to go". Disconnect one of the heating element leads while the boiler is doing the long fill.