When the PSV Valve is set to close the cleaner (to run the skimmer) when I turn on the pump the filter pot begins to fill with water then it recedes to empty. This continues indefinitely, so that I can't use the skimmer setting. When I set the PSV valve to close the skimmer (to run the suction side cleaner) the filter pot fills completely with water and the cleaner operates just fine. Anyone have suggestions about what this could be? I was thinking it might be the PSV valve itself. It is about 5 years old. Any help is appreciated.