Steve, that's it. It actually pushes the water back up the line. remember that your cold water line connects to the hot water heater. So when you push water back into the hot water line, it goes back into the tank which pushes the water back into the cold water line. All you have to do to achieve this is over come the line pressure, Hence the boost pump on the system. There is no valve on your lines either before or after the heater. AS you turn on your hot water line at the sink, water from the top of the heater enters the hot water line and cold water from the sullpy enters the bottom of the heater. So if you push water back down the hot water line, ie the waste water with a boost pump, you push water back into the cold water line and actually all they way back out to the main line in the street.
I did a bit of research on this a while back trying to fully understand the whole process. Found out it will not work for me as I don't have the hot water tank and thus would just be recirculating and waste water back into my house system. I do have a whole house 5 stage water softner system that also filters the water with carbon and such. It is a heavy duty comerical system that the previous owner installed. I've never checked my TDS but so far, I have no problems with either of my tanks.
I did a bit of research on this a while back trying to fully understand the whole process. Found out it will not work for me as I don't have the hot water tank and thus would just be recirculating and waste water back into my house system. I do have a whole house 5 stage water softner system that also filters the water with carbon and such. It is a heavy duty comerical system that the previous owner installed. I've never checked my TDS but so far, I have no problems with either of my tanks.