I have an above ground pool that I just finished a major overhaul on over the weekend. I replaced the liner, re-did all of the plumbing and changed the filter media and laterals. The filter is a Hayward S200 and I switched it from sand to zeobrite. The pool finally finished filling last night so I followed the directions from zeobrite and backwashed, rinsed, etc. Each time I did so, the filter seemed to operate normally and was around 5-7 PSI. After completing those steps, I turned the multiport setting to filter and it immediately built up a ton of pressure up to 25 PSI. Water was squeezing from the top air relief screw and also gushing from the waste line. Does it sound like the multiport valve could have gone bad over the winter? A couple of other symptoms are even with the valve set to close, water is backfeeding from the return line into the filter. I'm assuming the close setting should shut that off but can anyone confirm? Could a bad spider gasket cause the filter to build pressure like it did? There doesn't really seem to be many more parts inside these valves from what I can tell so I am at a loss as to what to look for.