I'll do my best to explain my predicament. I had a house built and installed Takagi TM-1 on demand water heater. It was located at the far end of the house away from the gas meter. We installed a Metlund "on demand" pump right off the water heater which was directly attached to a recirc loop. The pump is activated by buttons in the house and the recirc worked great. The problem was that the plumbers did not read the specs carefully and the water heater required more gas than could really reach the water heater so when the home gas heater was on the water heater would shut off and we would get stuck in cold showers.

To resolve that problem we moved the tankless to the other end of the house right next to the gas meter. The plumbers tapped into existing lines for hot and cold water, but there was no practical way to tie directly into the recirc line at the water heater itself. We left the pump at the opposite end of the house hoping it could "pull" the water through the recirc. The problem is now when we hit a button to activate the pump the pump kicks in and runs for three minutes before shutting off (built in max run time). I have verified that hot water never gets pulled through the recirc loop. It seems that the existing water in the lines is just following the path of least resistance and going in a circle. There is nothing forcing it to pull down the line that reaches the hot water heater.

Is there any way to make this work without moving the water heater or the pump and without tearing out more drywall to find the loop at that end of the house? Moving the water heater is not an option. It has to be close to the meter to solve the original problem. We could move the pump easily enough, but is there a way to take advantage of the recirc loop which we went to the trouble of putting in? I'd rather do that than recirc through the cold water line if possible. I imagine there may be more than one way to resolve this, but I'm just the homeowner. Unfortunately I seem to have a better grasp of the situation than my plumber who told me this setup should work.