Cleaning a hot water system

JHK

I am working on the hot water side of a steam to hot water heat exchanger. Hot water side feeds fan coils for offices and we found a couple of clogged strainers on the inlet to the coils. The strainers were packed with a substance like hardened dirt, I had to use a screwdriver to break it up to get out. The system has no auto-feed and the water is not treated and system is manually filled to 10 psi ( the coils are only on the first floor ) and the water temperature varies with outdoor temperature up to a high of 180 degrees. We drained out 10 gallons of water and it was a very dark brown. I want to propose a complete cleaning in May when it goes off line. What is the best way to clean out the hot water side of this system? As far as I know the heat exchanger (tube and shell) has never been cleaned and it is over 20 years old so is it better at this point to recommend replacing the heat exchanger because I could create a leak by cleaning it? Any advice would be appreciated. Thank you.

kcopp

A power flushing cart set up and a good cleaner such as Rhomar, Sentinel or Adey would be a good start.
If you can drain and refill the system w/ the cleaner in there a week before and let if circulate that would loosen up crud so the power flush could be more effective.

https://rhomarwater.com/Power_Flushers_Filters.html