I have a traditional roof solar heater setup that has a Pentair PTV-2TS solar diverter valve with a "leak down check valve" as its called. However, it doesn't seem to always be draining back to the pool. Can someone tell me if the valve will allow for drain back from the panels even when the diverter valve is turned to bypass and the system is off? Or will it only drain back to the pool when the diverter valve is positioned to operate the solar loop?