Mine is doing the same thing. It's 3 years old and the first year, it sucked the AF right up when set to "Winterize". Last year, I had a little trouble getting it to suck out of the jug. This year, I had a heck of a time. I had already drained my fresh tank, so I decided to put some water back in. I switched back and forth between "winterize" and "normal" in order to keep a prime on the pump. I had the jug up even with the winterizing connection. I eventually got it winterized. I'm not sure what is going on with mine also. I sure hate to hear that pump running dry while I run back and forth from one side of the camper to the other while trying to figure it out. Next year I may not be able to winterize it if it gets any worse. Like yours, my pump will suck water from the tank with no problems.