Right now I am thinking its the parker 3 way valve. Does that sound right to you?
In fact it should be a 2 way valve.
The Ducale came in 3 different models. The first ones had a "normal" 2 way valve behind the boiler. Later on it was changed to a valve on the right side next to the boiler.
The latest models have the refill valve under the drip tray. This one looks like a 3-way valve and is mounted on a piece of brass.
First check if the coil gets 110 / 220 volt a few seconds after you switched on the machine. (the pump should start running after a few seconds)
If there is current, remove the coil from the valve and stick a screwdriver through the coil. Switch on the machine and you should be able to feel the magnatism of the coil.
If both are ok, check if any water reaches the valve. Just remove the valve (on a cold and switched off machine) and turn on the water to the machine. If water comes out somewhere, it should be a blocked line between the valve and the boiler. Just try and error.
If you can post some pictures, I can point it out.
Frank