Thanks for the suggestions. This is 1300 sq.ft condo. The W/H is located on the poarch, the heat exchanger is in the middle of the unit. The W/H has one cold water line in, one hot water line out and one water line retuning from the heat exchanger. The domestic hot water line must be teed somewhere in the wall or ceiling ahead of the heat exchanger. To correct the problem and bring it up to code I will need to have two lines (in and out) from the exchanger to the W/H or boiler, I get that. However, I am not looking forward to ripping into sheetrock to add a new copper line. Having said that, if I leave the existing configuration are there any safety or health reasons that I am missing?