Just thought I would share a little mishap of mine from yesterday. It was time to backwash so I turn the valve to backwash as usual. After rinsing and returning the valve to the "filter" setting I noticed that it was still back washing the water. I could not get it to come out of backwash even though the selector was back on "filter". Once I opened up the top of sand filter this is what I found. I posted a picture of what the seal looked like before and after replacement. I thought this may help someone else in the future.