so it sounds like the fundamentals of this system should work, it’s just going to take more pressure. As I mentioned, the water does flow back to the heater with one pump. I cannot ensure that it has enough pressure to overcome the resistance of the 12psi pressure on the other side of the monoflow T but when I have shut off the incoming line at the ball valve just before the Back flow preventer, to make the loop all the more closed, the pump should be able to recycle the water into the “cold in” riser. If I try to purge some water from the hose bib at the terminating end of the loop, there is flow, I think I have air trapped in the lines and until I can adequately purge it out, there will always be that resistance. If I have dedicated pumps at either end of the series loop, one pushing and one pulling, maybe between the 2 expansion tanks and 2 air bleeders, it may just purge the air after running the pumps for a few hours with cold water. Appreciate the help, not sure what a “jetter” is but if it provides an alternate way to purge air. Furthermore, if you go to http://cowan.bendnet.com/volcalc/CylinderH.htm you can calculate the gallons that would be in 622 ft of 5/8 pex tubing to be about 10 gallons, add the rest of my system as approximately half of that and round up and you still have about half of the 40 gallon capacity of the hot water heater, in the piping. The unit should be able to keep up. The water return should drop the total temp inside the heater unit by half or ((150+75)/2)= 112.5 degrees after one full rotation of the water. It should build from there on upwards at maybe 5 degrees per hour? but again my concern is on flow right now, and this is probably hindering any positive outcome.