Water heater is full. I also tried running the pump with water pressure coming in from a water hose.
Faucet was tried open and closed (when system is dry after winter the pump will usually push a great deal of air pressure through the lines before water flows).
I found once piece of plastic debris, but that did not fix the problem. I just washed it out and found nothing.
I don't have a water fill valve, not sure what that is. My water tank gravity feeds the water pump when full, the pump is next to the tank, so sucks it when low.
I put diaphragm on without the rest of the pump head, ran it on the bench and it sounded very similar to the good sound, so I assume the motor is running at the right rpm.
I will try running it disconnected from the outflow.
thanks for the responses.