My fresh water pump does not seem to be hold its pressure or something. This is my first boat with running water and when i bought the boat it did not work. So I put a new pump in last summer and it worked fine all summer. This spring it has not been working, the pump sounds the same when it's running but does not pump the water. It pumps little water and lots of air...then just air shortly after. If I use the dockside water attachment(no pump) hooked up to the marina water it will work fine. Any idea's?