Troubled pump

Basically my problem is every time I vacuum everything goes right back into the pool. I have taken out the sand and taken the laterals to two different pools stores and they said they can't find any cracks. I put fresh sand in as they suggested and still have the same problem. We just purchased the pool August 2013.The one pool store replaced the spider gasket because water drained out the backwash hole when. It was placed on recirculated. It didn't change anything. Help!!
 
I wonder if the handle got reinstalled backwards or something when the multiport valve was overhauled. Then the ports wouldn't match what the handle said. You might be on recirculate when you think you're on filter. If it's a lateral inside, you'd see sand coming out the returns. Watch the pressure gauge on the filter when you're in different modes and see if they make sense. You can always post your test results here and let someone try to make sense of them.
 
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