I had this exact same problem: the pump wouldn't go 5 seconds without shutting itself off. I finally read online somewhere about the flexible bladder tank that others have mentioned on here. It also said to put the nozzle in, and then wait a bit before you start pumping. I suppose this equalizes the pressure, or something like that. But now I always put the nozzle in, wait just a bit, and then pump, and I haven't had this problem since.