water pump runs continuously

[JustinChase]

If my holding tank is full, all is well. Once the level of the water in the tank drops below the pump, my pump will start to occasionally run continuously, until I turn on a faucet, then it will prime and start moving water.


As the water level drops, it gets worse. Once I'm down to about 15% full, it won't prime and will just run continuously. If I get it primed, it will pump the tank completely if I let it. It's only when I turn off demand that the pump runs without priming.


I've replaced with a new pump but it does the same thing.


I called Shurflo and he said he has no explanation and no suggestions to try to fix this


I have checked and the inlet screen is clean, and it doesn't seem to be sucking air anywhere, and the pump isn't leaking.


I have no idea how to proceed from here.