We have been having a problem this year with our radiant heat system. It is a system using an outside wood boiler on an open loop which transfers heat to the closed loop system for heat by a flat plate heat exchanger. It has worked great for the last three years ...but this year it is not keeping up with our heat needs. I have come to the conclusion that the heat exchanger must need to be cleaned. We are getting a hug drop in temp in the heat exchange over to the closed loop. If anyone has any input on cleaning a flat plate heat exchanger I would appreciate it. After reviewing manuals etc it is suggested to use a phosphoric acid solution of 5% and preferably backflush it for an in place cleaning. However, I have Wye strainers ahead of the pump and just reversing flow goes against their flow. I really don't want to have to try and turn them around etc. ...and right now pulling the heat exchanger in the middle of winter will be a major undertaking due to the lack of foresight to allow for this. So unless back flushing against the strainers is not a big deal ...I guess I am forced to go with regular flow with the phosphoric acid solution etc. Then ...I find today that finding the phosphoric acid locally is a little bit of a problem. Has anyone ever used CLR to do this process? That I know I can get locally. If I have to get the phosphoric acid it looks like I may have to have it shipped in. I know that CLR is not the same thing ...but will it work? Again ..any suggestions are much appreciated. Thx RH