I have an issue with my sand filter. When I stop the pump to clear the basket or backwash on occasion it will start to pour water out the pressure release points at the top of the filter. (see pic)
Sometimes it will seal up and not leak but other times it seems to build up pressure and leak. I try letting air into the basket, openning sand filter drain, backwash, go to waste etc. Lately I've been putting it into recirculate and bypassing the filter. If I leave it that way for a few hours I can usually move it back to filter and it will flow without leaking. Sometimes when I turn the pump off when it's leaking I get a back flush of water into the skimmer boxes.
I purchase a new seal for the top of the sand filter (it's about 2 years old) but haven't torn into the piping to put it in yet. Guess the other thing could be the sand is full of junk on the top? Live in Iowa with 3-4 month swim season should sand be changed after 2 years?
Any advise on what could be the cause of this? Advise on a resolution?