Is this a multi-port valve offering back wash, no filter, rinse, etc. modes? Have you ever turned it counter clock wise? (Never turn it counter clock wise.)

You will need to remove the top and put a new gasket in the valve.

If it is Push Pull, remove the two screws at the top and pull the assembly out. Remove and replace all "O" rings. Lube with silicone grease for pools and reassemble.

I think this will fis you up.

Thanks for your question today.