Looking all over the place for a solution to my problem. Even though I've installed a check-valve, my system "flows" the wrong way at night, sucking hot water out of the tank.
I have a Radco DBX type drainback system connected with AET panels on the roof. The Radco is a drainback tank with integrated heat exchanger, mounted on the floor next to the water heater, 2 pump setup -- one on the collector loop, one circulating water from the HW heater to the heat exchanger.
During the day, the system works perfectly. Sun heats the collectors, collector-loop pump works like it should, drainback tank gets hot, circulatory pumps circulate domestic water through the heat exchanger and it heats up. At night, however, the flow reverses... how water leaves the HW heater, circulates the reverse way through the circulatory loop (out the top of the HW heater, through the heat exchanger, into the bottom of the HW heater).
In other words, at night, I lose some of the BTUs I gathered during the day. I've installed various swing/spring checks, but they don't always shut-off the reverse flow (and, eventually, they go bad and get stuck in the open-position... i guess oxygenated hot-water is a bit corrosive)
Anyone have an idea how to stop the reverse flow? Do I need to mount the drainback tank above the HW heater?
PS -- just to be clear -- no flow at night through the collectors. Thermo-syphoning is only occuring on the HW --> heat exchanger loop.