fresh water pump runs but won't prime and push water

W/ the huge amount of information the op gave on this problem, should be a pc a cake !!

Lets spell it out for you,.........
Was it working fine, then quit midstream ?
Dija run out of water, refill, and now have the problem ?
Dija just remove & replace the pump, or change any pluming incl filter ?
Dija just drain the water heater
Dija know that if water can't get outta the pump, water can't get in ?

Another possibility - check the inlet filter. Sometimes that can get plugged up which prevents water flow - mine was filled with plastic shavings likely from the holes Fleetwood drilled into the plastic tank when setting up the FW tank.

Is the water heater completely filled, or still trying to fill? Is the relief valve open on the water heater?

What is make and model of rig?
Fill valve in wrong position
Winterizing valve in wrong position.

I've had this happen three times over the years. In those cases it was caused by the pump sucking up some tiny piece of debris. Take the head off and rinse the parts off under some running water (irony!).

tpnysted wrote:
The tank is full, the pump runs but won't move water. Any suggestions?

If you have NOT changed anything(valves) since you used the Pump last, odds are the pump diaphragm is bad. The BEST way to check the pump is to disconnect the Inlet line at the pump from the water tank, connect a short line to a gallon jug of water and see if the pump pulls the water. if it does NOT, replace the pump. Doug

IMHO, there is probably a leak, not allowing the pump to build pressure.

Mine wouldn't go once a few years back.
I wound up pulling the intake side off and priming the pump.
Only ever happened once.

Try opening several faucets for about 30 seconds.

Do you have the valve closed that causes the system to build up pressure and not to just pour water back into the tank.

It's a pretty common cause of water circulating, and not building up pressure.