Thanks Jim L, Elaine and Bill,
Jim L,
It turns out the clear plastic filter screen on the input side is OK, and I took it off the old pump and put it on my new pump which works well in my test setup. Wiki shows me how the pump works-
https://en.wikipedia.org/wiki/Diaphragm_pump
I took it apart last night, but couldn't see anything obvious. Anyway, my new pump works and the remaining problem is the water leak at the city water flange.
Elaine and Bill,
With the board under the couch removed (it was screwed down) to replace the pump, I could see the tubing and diagrammed the fresh water and city water plumbing. There are no valves- lots of elbow and two tee connectors- but no valves. Without removing the hot water tank I can't get to the tee connectors and loosen the tubing so that I can replace the leaking elbow connector inside the city water cutout.
Question. I may have to remove either the hot water tank or the outside fiberglass wall in order to replace a $4.00 part. How difficult is iy to remove the tank or the outside fiberglass wall where the city water cutout is? What else should I knon before attempting it?