You probably drained the water tank when you winterized. Maybe put a little anti-freeze in there. I am guessing you have an air lock between the pump and the refilled tank. Mine does that but usually will prime if the tank is full.
To solve that problem I have to get the air out of the line between the tank and the pump. On my boat there is a place to disconnect the hose in front of the pump. I fill the hose leading to the pump and simply blow into it. Do that a couple of times, reconnect, and the pump is primed.
Another thing that can happen is a loose connection. I have had to isolate plumbing problems by limiting connections. I can block off the hot water for example. Or start with just the galley sink eliminating everything else including the hot water tank. But I am betting it is just a prime problem. Make sure the tank is full and the vent is clear.
P.S. In all this I assumed that you know the pump is running.
