I have the same model and can’t get it to hold pressure. I changed the pump. When I pump it up pressure builds but bleeds down quickly. Do you have any guess at what it might be?
Discussion
Easiest way to find the leak is to run the pressure up and submerge the fount in water. It’ll present itself immediately. Probably an easy fix too.
Most likely culprit is the gasket on the filler cap. Next bet would be the valve assembly needing a little tightening.