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Boiler wash out?

Champ6 Member Posts: 20
Just a home owner here, not a pro. My house has a 12 year old Weil McLain steam boiler. Every week or so I do flush the low water cut-off, as the installer recommended.
As a side-story, I've recently been volunteering on the restoration of a steam locomotive (N&W's 611) and learned a lot about locomotive boilers, which need frequent wash-outs because of the volume of water consumed, and the general quality of the feed water, which was often pond or stream water with lots of sediment.
So back to my question, since a residential boiler does not require much feed water and it is domestic potable water, does my boiler need to be washed out, and if so, how frequently?


  • BobC
    BobC Member Posts: 5,473
    If a system has been skimmed and the water is free of oils and other contaminants it should never need to be washed out. A steam boiler needs very little fresh water unless something is leaking.

    The weekly flush of the LWCO should be fine along with periodic draining of the mud leg drain to keep the bottom of the boiler reasonable free of crud (drain water till it runs clear). Make sure you run the boiler up to steam after adding any fresh water to drive off any oxygen in the fresh water. Also be careful adding water to a hot boiler, do it very slowly so you don't shock the castings.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Champ6
    Champ6 Member Posts: 20
    Thanks, Bob. The installer never mentioned draining the mud leg. I just googled that and got an article by Dan Holoran, so will give it a shot. Thanks again.
  • Jamie Hall
    Jamie Hall Member Posts: 22,972
    There's a world of difference -- and not only in size. Your 611 (and she is a beautiful engine, and I'm so glad that you all are going to get her in steam again!) uses a huge amount of water as she runs, and it all goes into steam and out the stack. Trouble is, of course, that anything that doesn't boil -- salts, mud, anything -- gets concentrated in what little water is left, and as you know if you don't blow the boiler down regularly (not just for the fans!) and wash it out regularly, it gets pretty goopy in there and, if nothing else, foams.

    But... if a residential system uses more than a gallon a week, that's probably excessive (mine uses more like two gallons a year!), so you just don't have the same problem at all. In fact, the less water you add the better -- so keep your flushing of the LWCO to the absolute minimum, and flushing the mud leg of the boiler (if there is one) to once a year, max, and again use the least amount of water possible.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Champ6Dave in QCAZman
  • Champ6
    Champ6 Member Posts: 20
    The 611 had a wonderful season this year, but it was short. I was part of the first washout after the initial firing, and rain gear wasn't that helpful. Youtube the blowing down of the lines and cylinders at that first firing too. Whew! After receiving new front truck (next week in fact) next year's season should be much longer. Thank for the advice on the mud leg too
  • Dave in QCA
    Dave in QCA Member Posts: 1,785
    I have been pondering the comments on this post for several days. While I agree with the observations and reasoning, I come to a slightly different conclusion.

    I think many boilers do OK without being washed out. The question is whether they would do better if they were washed out. Even in a very tight system where only a gallon or two is added over the course of a season, there may not be an accumulation of scale causing lime, but there will be some accumulation of "mud" in the bottom of the boiler. We see this in the bottom of float type LWCO devices, and of course, we flush those out. Every few years they should be opened and completely cleaned.

    But what about the mud that will collect over time in the bottom of a boiler? Flushing out the mud leg does keep that passage open, but I don't think that is enough. When one considers the irregular surfaces present in the bottom of a cast iron sectional boiler, there is a low spot in every section where mud will accumulate. Flushing the mud leg will not remove it. The only way it can be removed is through the use of a spray wand spraying water into the recesses, churning up the mud and rinsing it out.

    How important is this? I have to say that I don't know. But consider an atmospheric fired boiler. The fire is right below the dirtiest part of the boiler and if that mud gets thick enough, it would allow the cast iron to get hotter than it should, and would reduce the life of the boiler. On a wet base boiler, such as my WM 680 or Jamie's WM 580, the mud will be sitting on the cold bottom surface and not on the fire side. I still see no harm in flushing out the mud; it can only have a good effect. Of course, this all assumes that when the fresh batch of water is put in the boiler that it will be brought up to boiling and will be held there for several minutes, to assure that the O2 will be driven off.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • PMJ
    PMJ Member Posts: 1,265
    I think Dave is probably right that a complete flushing very few years is not a bad idea and certainly won't hurt anything.

    As far as how serious the mud on the bottom problem is I'm not sure either beyond my own experience which suggests not much of a problem left alone. As long as the boiler still drains on both sides I doubt is is very deep. And judging by the bit of mud that does come out of mine (only on the closest side to the wet return by the way) it is difficult to picture it as hard enough to form an actual insulating layer inside. My guess is that during firing it is pretty loose and moving around with the water. But of course this is just speculation on my part as I can't see in there. My boiler has pretty deep pockets on each side well out of the fire area which I assume aren't completely full of mud if they still drain. Maybe some of the pros would comment about how many failures they have seen on the bottom that they would attribute to mud inside.

    One thing is for sure. Mud in the bottom can't be helping anything.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
  • wcs5050
    wcs5050 Member Posts: 131

    Dan suggested I watch this video when I asked about this subject.