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Cleaning sediment from boiler bottom

My boiler water is continuously dirty, even after a thorough clean and skim by a professional, and it's affecting its performance. The water in the sight glass is clean when the boiler isn't working but dirty (brown) when working. If I open the lowest possible drain valve (red handle in pic) when the boiler isn't working, I get clean water. If I open the valve just after the boiler has shut off (sight glass water still dirty and hasn't settled yet), it's dark brown like melted chocolate. I could do this daily and drain gallons of dirty water. Which I am hesitant to do since I have to reintroduce fresh water (cold) every time.

My question: how does one drain the boiler from the very bottom of it, to get the sediment that has settled to the bottom? I thought this is what the drain valve I currently have (red handle) was, but I now believe that it is actually above the boiler bottom since when the boiler is off and has cooled a bit, there is sediment that has settled below the opening of the drain valve and thus doesn't drain out when I open the valve. Then when the boiler gets turned on, all this sediment I couldn't drain out gets mixed up into the water again, affecting performance.


  • BobC
    BobC Member Posts: 5,478
    The valve below the sight glass is probably as low as your going to find, also use the other valve on the boiler water return to get the crud out of the return. If the return water is real bad consider feeding water into the main vent pipe fitting to flush the line out.

    This is from the Peerless boiler manual and is probably good for any steam boiler that needs cleaning. you can chemicals to a boiler through the pressure relief boiler tapping with a short piece of hose and a funnel. Be careful working with very hot water with chemicals.

    1. Clean the boiler within one week after initial start-up.
    Cleaning will be more effective if boiler operates a
    day or two to loosen sediment and impurities in
    2. Boiler must be cleaned to remove any accumulation
    of oil, grease, sludge, etc. in the system. These
    substances can cause foaming and surging of boiler
    water, producing an unstable water line and water
    carryover to system.
    3. Connect a skim valve off the 1-1/2 NPT skim tapping
    on rear of boiler. See Figure 7.1 (Section 7) for skim
    tapping location. Run a 1-1/2 NPT drain line off
    skim valve to a point of safe discharge.
    4. Provide a means of supplying continuous fresh water
    to the boiler for the cleaning process.
    5. Use common washing soda, such as Arm and
    Hammer Super Washing Soda. Mix 1/2 pound of
    soda with water in a 10 quart pail. Pour the mixture
    into the boiler through the safety relief valve tapping.
    6. Open the skim valve. Fill boiler until water begins to
    flow out of the valve.
    7. Turn on burner. Allow boiler water to heat up to just
    below steaming (180 - 200°F). Do not allow boiler to
    steam; steaming mixes up contaminants instead of
    floating them at surface.
    8. Open make-up water valve to continually feed water
    to boiler. Adjust flow to maintain water temperature
    at 180 - 200°F.
    9. Continue skimming boiler until water flowing from
    skim tapping flows clear. This will take some time,
    possibly several hours for a dirty system.
    10. Turn off burner, close make-up water valve.
    11. Drain boiler completely. Refill and drain one or two
    times to wash out all washing soda.
    12. Remove skim valve and piping. Pipe a nipple and
    cap in the skim valve.
    Cleaning the boiler requires the use
    of very hot water and corrosive
    chemicals. Use care when handling
    to prevent injury.
    Do not leave boiler unattended while
    firing burner. Operating boiler with
    water below minimum permissible
    water level may fracture sections.
    Do not allow make-up water to flow
    too fast. Excessive quantities of cold
    water may fracture sections.
    If gauge glass becomes dirty more
    contaminants have worked loose in
    system. Repeat cleaning and
    skimming process as needed to clean the

    This procedure might have to be repeated to get everything out.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Where does the 160 gph come into play?
    This is a situation where washing with a wand would be more effective.
    I simmered the washing soda solution, by cycling the burner off and on by the switch, while skimming with a small amount of makeup water entering the boiler. Then I cut off the burner for good, and continued skimming until the outflow ran cold. My theory was that the hot oily water had floated on top of the cold, and flowed out the skim port. It still took a long time.--NBC
  • heatinghelp819
    heatinghelp819 Member Posts: 72
    I don't think this is an oil (on top) issue - I think it's a sediment settled on bottom issue.

    I tried draining the wet return through that valve in the back of the Boiler, but after a little bit of brown water from the wet return, I get clean water from the boiler coming thru the Hartford loop (I posted about this a week or so ago and was told this is normal). I'm wary of flushing the wet return with a hose because it's a very old house and I'm afraid of loosening sediment and uncovering holes that will cause leaks, as I've read on this site can happen when flushing wet returns. The wet return is mainly behind a wall so I wouldn't be able to get to those leaks very easily...

    Just want to be able to clean my system so that the surging can finally stop.
    EBEBRATT-Ed Member Posts: 15,527
    Best skimming & cleaning IMHO is Dan's method in LAOSH. You don't need to keep the burner running.
  • Koan
    Koan Member Posts: 439
    I found that a Gerry Gill wanding was the only way for me to get my boiler clean. Also you mat want to undo the union going to the Hartford loop and check the wet return there for occlusion. Mine was nearly closed with gunk. Maybe the wet return could use a wanding as well?
  • SteamCoffee
    SteamCoffee Member Posts: 123
    I did the Gill method with my moms boiler, a nearly 30 year old boiler...used a Hotsy steam cleaner with a tip, I bent to go about 90 degrees or so...took for ever...the runout looked like sewer water at first...awesome results providing you can get easy access...highly recommended!
  • Dave0176
    Dave0176 Member Posts: 1,177
    Hi all I was the one who cleaned the boiler previously. Upon arrival I added a skim tapping that didn't exist, I proceeded to wand wash the boiler till clean then skimmed with Brian's skim tool for a while. I did drain the wet return. The wet return runs about 45' below the water line in a finished basement buried behind a Sheetrock wall. I pulled all the controls off and cleaned them.
    DL Mechanical LLC Heating, Cooling and Plumbing 732-266-5386
    NJ Master HVACR Lic# 4630
    Specializing in Steam Heating, Serving the residents of New Jersey


    I cannot force people to spend money, I can only suggest how to spend it wisely.......
  • porcelli
    porcelli Member Posts: 1
    edited September 2021
    I have a four year old residential steam boiler. My old boiler had a skimmer valve on it. The plumber who installed the boiler told me this new boiler didn’t need a skimmer because skimming was not needed in the new boilers. Every year I struggle with dirty water in the boiler. What should I do. Thank you. 
    Ps. I have the same set up as heating help 819. 
  • DavidDow_2
    DavidDow_2 Member Posts: 11
    I'm glad you found this site, and you will be too.
    It's sad to hear about your issue with a 4 year old boiler. This type of work ethic is common, unfortunately. I see it a lot.
    I worked for a company 12 or so years ago. The owner had 3 steam boilers to install and all got installed wrong causing considerable trouble. He would not allow me to intervene and didn't like my input. I was let go. Went to work for myself.
    I have a new account with 2 steam boilers and a hot water boiler my former employer installed. Many problems that need many dollars to correct. The customer does not have the funds to fix.
    I'm not sure where you live, but some of the folks here may direct you.
    Best to deal with someone with steam knowledge, like a gray haired old timer!