I've got an indirect-fired water heater where the exchanger coil is inside the TANK, NOT within the boiler as is described elsewhere on this site. It slaves as just another zone on the boiler. The water in my town is extremely mineral/iron-rich (YES, I'm going to install a softener). I do have a 15 micron filter on the feed to reduce the sludge coming from the main. This water heater is only 13 months old and set me back $800 then. It used to recover in 10-15 minutes, now recovery time is several HOURS. The in/out of the exchanger are about the same temp, so I'm certain there
must be a pretty impressive layer of calcium/rust on the exchanger. The instructions provided with the heater say to use Phosphoric Acid to clean this coil. ...where on this planet can a do-it-yourselfer get his hands on phosphoric acid??? Is there another way? I've been tempted to remove the coil (risking a leak upon reassembly) and either replace it (I do have the P/N) or try electrolisis. My biggest concern is that the heating system side of things (the same water that flows through the exchanger) contains at least some lead-solder in older parts of the home. Is there a risk of the acid burning through the copper so as to allow for this potentially lead-carrying water to be introduced into the domestic HW??? Should I just write this tank off as a loss and install a new one when I do the softener? Inquiring minds want to know.