I live in a cold area of upstate NY and recently (October 08) installed a WF Envision 064 with a closed loop. I am having problems with low water flow which I believe is because of freezing up of the lines. I base this on I am supposed to have 7 600' lines, but one had a leak and was shut down early on. Another developed a leak during operation and went undetected for some time - 3 to 4 weeks maybe. That line was corrected and is fine now. My system automatically adds water and is the main reason I didn't detect the leak. So operationally I have 3600' of loops vice 4200', and I don't know how much the antifreeze was diluted. The unit will lock out because of the low flow when operated during heavy heating loads. It works fine when conditions are milder. The antifreeze came precharged in the lines, and my contractor installed the lines in the loops and I added water from my well. I know I have lost antifreeze, I just dont know how much. The antifreeze is or was an ethanol concentrate to protect down to 10F. So, I can use any advise out there especially on or about antifreeze. Where can I get it, How do I add it, and where do I add it, I can add fluid at either supply or the return sides if I knew how. What is the best way to test the concentration. I have read info about a GT Flow Center that is non-pressurized, and useful to add antifreeze, but they are a lot of money and I already have a flow center. Any thoughts?