Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Cast Iron Radiator Sludge

So I bought a used cast iron radiator for my hot water heating system. I took off the old fittings and found, what might be called, sludge inside. I've looked through the posts and it seems that when sludge is brought up it refers to something that can be easily flushed out with water. The stuff in my radiator is a black, greasy, clay-like substance and I don't think any water will flush this out. The unit is not packed with this crud tho and I can poke a rod from the inlet through to the outlet. There was one post mentioning running a cleaning solution through a heating system to get rid of sludge. There was also mention of using a drill powered pump to circulate the cleaner. So do you think if I set up a little closed loop using some fittings, a drill pump and whatever that i can circulate enough cleaner, through this radiator, to get rid of the "sludge"? Or should I connect it to the system, as is, since water seems like it should be able to flow through the unit anyway? The rationale being that the sludge will just stay where it is. Or is there a plan "C"? And what cleaner would work best in this situation?


  • PC7060
    PC7060 Member Posts: 781
    Since you’ve already got the unit out and ends off, I’d just use a pressure washer wand to clean the gunk loose. Then use hose to flush any remaining gunk out. 
  • KennethGoetz
    KennethGoetz Member Posts: 6
    You most likely have sludge called magnatite, which is a iron type of bacteria…that can be flushed and you must put in a magnet type dirt separator on the horizontal return line and treat the boiler system water with a cleaner that will balance the pH around neutral of 7. …. And service/ clean the magnets on a regular basis 
  • KennethGoetz
    KennethGoetz Member Posts: 6

  • KennethGoetz
    KennethGoetz Member Posts: 6
    Example of magnetite in a boiler block
  • DustyG
    DustyG Member Posts: 2
    I'm liking the idea of the power washer but not the idea of dragging a 14 tube cast iron radiator to the backyard. That's a task you don't find too many volunteers for. But it's a good idea which I will try.

    And thanks to KennethGoetz for the picture and info.
  • PC7060
    PC7060 Member Posts: 781
    I used a checkbook to move my radiators! 😅

  • pedmec
    pedmec Member Posts: 290
    i hope you got a good price on that radiator because you could have bought a new one.
  • hot_rod
    hot_rod Member Posts: 16,875
    It wold be nice to have it outside to flush so you could flip it a few times to get a good clean out

    If the sludge is oily you will need to run a cleaner. The hydronic cleaners are a strong detergent to dissolve the oils.

    If the stuff that flushed out sticks to a magnet you have some magnetite that may never flush 100%. So a mag filter on the system as suggested.  I doubt you could ever get it back to bare metal without an internal sand blast😉
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • kcopp
    kcopp Member Posts: 4,010
    edited September 27
    Get as much of that spooge out as you can before adding it to the system. Once that stuff gets in it will be along process to get it out.
    A "wand" on a hose w/ hot detergent laden water will go a long way to get it out.
    I just did this to a system this past fall. About 6 old rads. I physically got a bunch of junk out. They were BIG rads that the homeowners lugged in. I did not take them back out.
    Needless to say even w/ a magnetic filter the system was filthy for a long time.
    I still need to go back this autumn and use a powerflush cart to clean it out.
  • PC7060
    PC7060 Member Posts: 781
    edited September 28
    pedmec said:
    i hope you got a good price on that radiator because you could have bought a new one.
    That was a original radiator was being taken to be sandblasted and powder coated. Returned safely back after a couple weeks by the same skilled movers.