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WM 78 series steam water / mud leg bound up

Have a Weil McLain 78 series steam boiler. I'm replacing the seals that are rotted out- the wet return/ mud leg ( bottom most water passage about 3") is plugged solid with thick sludge that I litterly have to chisel out with hammer drill. I can get the passage cleared out but obviously there is much fouling beyond what's readily accessible- apparently the chemical treatment did no good. I've heard once I got it back together I can circulate muratic acid to clean it out but onl heard have never talked with anyone who's actually done it. Was thinking of rigging up some piping system using an old hot water heater as a receiver of sorts and circulating with a small pump like bg nf22 or whatever and keep blowing it down till it seems clean. do U think the pump would hold up to the acid? Who's done this with success? When I say plugged I mean plugged solid like concrete- even though I have it apart replacing all the sections isn't an option. See attached pics. Please advise. Thanks


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    edited September 2013
    Constipated boiler

    Are new sections unavailable, or just beyond your means at the moment?

    Muriatic acid would be too strong for this cleanout-best to try vinegar, which will be less aggressive on the cast iron.

    These deposits look like the result of too much fresh water being added constantly to compensate for a leak somewhere in the system. What sort of chemicals were put in the boiler?

    Unfortunately, there is little chance of success in this case, but keep us posted.--NBC

    What chemicals were in the boiler?
  • dave1234
    dave1234 Member Posts: 16
    Constipated boiler

    Your right on. It's actually used as a humidifier for an ahu so yes it is constantly adding mu water. We had a chemical process at one time few years ago unsure of the exact chemical but I could find out. I've been told the muratic acid is the key but u say its to strong. What about muratic acid replacement like green envy?
  • Cleaning boilers

    The problem with muriatic acid is the presence of chlorides which react badly with the cast iron (see graphitic corrosion).

    Do a search for Rhomar boiler chemicals and ask them about what would be best.

    How old is this boiler? What about new sections? What size is ir?--NBC
  • Rod
    Rod Posts: 2,067
    Hot Tank

    Hi - Acid and cast iron AREN'T a good mix! You might see if you can find someone with a "hot tank", like either a car radiator shop or a machine shop that  does a lot of auto engine rebuilds. Hot tanks use boiling water with a high concentration of Sodium Hydroxide. "Hot tanks" used to be pretty common but due to EPA regulations are now harder to find.

    - Rod
  • dave1234
    dave1234 Member Posts: 16

    Replacing sections is questionable due to cost of course.
  • dave1234
    dave1234 Member Posts: 16
    Data tag

    Here's a picture of the data tag
  • SWEI
    SWEI Member Posts: 7,356
    Constant makeup water

    is hard on boilers.  http://www.heatinghelp.com/article/323/Boilers/141/Billy-and-the-Baker is probably worth reading.

    There are also boilers designed specifically for this type of service.
  • Hap_Hazzard
    Hap_Hazzard Member Posts: 2,849
    You're absolutely right!

    HCl is not only hard on metals; it's not that great for people either.

    I use muriatic acid all the time--in my pool, for etching concrete, etc.--all outdoor applications. Even I'm not crazy enough to open that stuff up in the house. When it reacts, chlorine gas is evolved. In an enclosed space it can be deadly.

    But to emphasize your point, I've learned from experience that I can't keep metal tools or parts in the shed where I keep my muriatic acid. If anybody is skeptical I can show them a bag of stainless steel hose clamps that got destroyed by muriatic acid vapor, not to mention all the rusted steel and the aluminum that's been turned into white powder.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • dave1234
    dave1234 Member Posts: 16

    Decided to go ahead and try the muriatic acid treatment- worked very well. Took sections apart and soaked because I had to replace rotted seals anyway- only adverse effect was weakend threads and had to use helicoils-'piping tap threads were ok. Must say worked well without any other adverse effects except for weakend threads. Just fyi
  • Rod
    Rod Posts: 2,067
    Plugged Boiler Section

    Hi- Thanks for the update. I'm glad it worked out for you.

    - Rod
This discussion has been closed.