I have a Polaris Caretaker system with the 5 port valves. Recently, when I turn on the pump it starts to push water into the "pre filter" just before the pump, but it never fully pressurizes. Then, after a minute or two, all of the water will suck out of the "pre-filter" basket housing and then this cycle starts again. Due to this "phenomenon", my pop ups never engage. I see no signs of leaks.
I'm wondering if it sounds like the pressure relief valve is bad? What are typical signs of the pressure relief valve going bad? Any other ideas would be greatly appreciated. Thanks.