Originally Posted by CapnRon47
When I got home I took apart the 'old' pump and found 4 of the six impeller blades still in the pump but un-attached. I am assuming the other two are working their way up into the heat exchanger and will eventually plug the mixing elbow. So I plan to back flush the heat exchanger to see if I can clean it out. Any thoughts, comments or suggestions on this procedure. I had not planned to open the end face plate of the heat exchanger, just flush it using the output and input hose connections. But I could be convinced otherwise.
Unless you've already made this effort and my comments are redundant, simply back washing with a garden hose to the output side of the heat exchanger and a hose to a bucket on the input side should wash out the "bits 'n pieces". If they do not appear, check the hose between your raw water pump and the heat exchanger as they may be lodged there.
Once you've recovered the debris, to clean out the tube bundle itself, you can use a cleaning agent like RydLyme or Barnacle Buster in a bucket with a small inexpensive submersible bilge pump ($29.00 at WM). A hose from the pump is connected to the discharge side of the heat exchanger and the hose from the input side is led back to the bucket. You can power the pump with some jumpers led back to your house bank. By recirculating a solution of RydLyme in this manner, you will remove most of the scale that may/will have built up in your tube bundle. If you are worried about debris being recirculated, a couple of wraps of cheese-cloth around the base of the submersible pump makes a pretty efficient filter without obstructing flow. You can test the efficacy of the solution by dipping a shell in the bucket. As long as it "fizzes" the stuffs still good. Four to six hours should be more than long enough with RydLyme although there is a table of recirculation times on the company's web-site.
In future, hang your ignition key on the handle of your raw water through hull.