We have a Pentair DE filter (FNSP60) with a Pentair multiport valve (SM-20-3). The pool was installed one year prior by the previous home owner. DE is inside the grids. We replaced the entire grid unit thinking the DE was getting inside because the grids were busted but the grids filled with DE again. Today, with the filter cover off, I placed the multiport valve in the filter position and turned the pump on. Water entered inside the grids and puffs them out. I'm assuming the water is entered the filter incorrectly. The spider gasket on the multiport valve is in placed and in good condition. Thought maybe the handle on the multiport valve was incorrect so removed the pin and changed the position of the handle. Water then entered the filter at the bottom but then exits on the ground as though i was backwashing.
I'm wondering if the pool was piped incorrectly at installation.
Thanks for you'll help!