I have 2 heat exchangers running this year to boost efficiency in the house. One exchanger is running perfect. Hot water goes in, and roughly 10 degree cooler water comes out. The 2nd exchange is not doing anything. Hot water goes in, hot water comes out. There is absolutely no change in temperature between the 2. Both of the pumps (014 taco) are working, the blower is working. The second exchanger is not clogged, and there is not any air trapped. Does anyone have a suggestion on what could possibly be going wrong?