My 2 zone indexer won't cycle between the zones. I thought it was a faulty old indexer so I took it apart and cleaned it up but that didn't take care of the problem so then I replaced it with a Fimco model and it's doing the same thing. The indexer is running straight from the lake pump to the zones...should there be a valve somewhere in between that releases the suction pressure when it's switched off? Any ideas would be appreciated.