Water pump

Winterizing valve in wrong position
No water in tank

Yep, I would go here first.

Check the connections between the pump in the tank to make sure that none of them are sucking air. I had that happen before after everything sent dry for a while.

wa8yxm wrote:
If it's spitting air then there is a leak on the inlet side of the pump.
One thing people often forget when winterizing is the water pump inlet strainer.
It may be cracked.

Another thing RV specific On my Rig there were a couple of quarter turn valves "up-line" (Tank side) of the water pump. One was a cut off valve, the other the Tank Drain valve. if I left that 2nd vlave open... What you have is what I'd get .

X2 on the pump strainer. Every cold winter, winterized or not, the plastic strainer covers would freeze and cause what the op described. A few bucks and problem solved.

If it's spitting air then there is a leak on the inlet side of the pump.
One thing people often forget when winterizing is the water pump inlet strainer.
It may be cracked.

Another thing RV specific On my Rig there were a couple of quarter turn valves "up-line" (Tank side) of the water pump. One was a cut off valve, the other the Tank Drain valve. if I left that 2nd vlave open... What you have is what I'd get .

The fresh water tank is full and I have a tankless water heater. No hot water tank to fill. Tomorrow I plan to run a line from the intake side of the pump to a bucket of water to check the pump.

Winterizing valve in wrong position
No water in tank

Or you tried it with just a hot water tap and the water heater tank is not full yet, so it spits.

Did you open a valve while the pump runs? My pump often will not prime after sitting in storage unless I open a faucet.
Otherwise may have a pipe issue on the inlet side of the pump.

Do you have water in the tank?