TP wrote:

Thanks, the installer retired. I have checked the manual and the
pipe dia and length are fine. I took a shop vacuum to both
pipes, just to be sure. Now the problem has seen to gone away.
The only thing that I noticed was there was not a screen on
the intake pipe. The manual doesn't specific any size of screen,
but shows a picture of one. Could I use standard window screen?
Or something heavier gage?

I'd suggest hardware cloth, with the 1/2" mesh.