I added a heat exchanger to my radiant system. Do they have some governor or something that regulates heat? I can create 140, 165 or 180 degree water with my tankless, yet only 120 degrees comes out of the heat exchanger and into the floors. If I pump 100 or 110 degree water, it pumps 100 or 110. So something is making it regulate at 120 degrees. I know it's creating the hot water at those temps because it also runs the taps and I measured them. It's a heat exchanger/closed system with one heat source. What could it be?