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Weil Mclain Boiler - Dissappearing Water

ALIGA Member Posts: 194
Hello All,

I have a Williamson boiler (rebadged Weil Mclain) one pipe parallel flow system.

I have a dissappearing water issue.

The boiler is using both risers into a dropped header(boiler picture was taken before drop header installed). The boiler does not cutout on pressure only turns off when thermostat is satisfied.

When the boiler is off - water is at normal level - approximately at the half mark on the glass gauge

When the boiler is starting to make steam - water dissappears and is not visible in the

glass gauge, but I dont beleive is low enough to trigger LWCO.

When thermostat is satisfied, water slowly comes back to the gauge to normal level.

I have about 2 feet of horizontal return piping below the water level behind the boiler.

Please let me know if this low water issue can damage the boiler, and ways I can try to resolve it. Thank you in advance.


  • BobC
    BobC Member Posts: 5,477
    edited October 2013

    What pressure is the boiler operating at? Does the water line bounce up and down a lot before it disappears from the gauge glass?

    If there is a lot of bounce the boiler might need to be skimmed.

    You may have a clog in the return pipe that is not allowing water to get back to the boiler easily. Is there a valve on the boiler return piping so you can flush the line; maybe you can feed water into a main vent and catch the water as it comes out of the return piping valve. If there isn't a valve on the return line it might have to be taken apart, the piping snaked out or replaced and then put a valve in when you put things back together.

    This should be fixed soon because it's just going to get worse and it's not good for the boilers longevity.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
    ALIGA Member Posts: 194

    Boiler is operating at around 1.5 psi.

    No bounce, it just looks like it gets sucked out when the steaming occurs.

    I dont beleive it is a clog, as the water does return when the boiler goes off. I am wondering if the water is hiding in the horizontal piping, but there is not that much pipe there. I did recall reading a post by NBC that he did have a similar issue.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Hidden water

    The problem I had was water hiding in a horizontal section of the wet return whose height was just above that of the normal water line. When the pressure rose, the boiler water was pushed into the return, and up into this pipe which held a lot of water due to its length.

    What is the height of your return in relation to the water line? Was the boiler skimmed after the repiping was done? There can be a lot of oil on newly threaded pipe, so that is more likely the source of the problem. Have the radiators sounded different since the piping (water in them)?--NBC
  • Bio
    Bio Member Posts: 278

    Sounds like more skimming is needed, skim for couple of hours then flush out, fill and flush a couple of times, last fill bring it to a boil, you may have to do this a couple of times
    ALIGA Member Posts: 194
    magic wand

    i will put together a wand, and flush the boiler out.

    i have to get a pump, as i dont have any floor drains.

    thank you all, will keep you posted.
  • ChrisJ
    ChrisJ Member Posts: 15,658

    I agree, use the wand and get the boiler good and clean. Also skim for a bit during the refill after using the wand just to be sure.

    After that I bet your disappearing water will stay put.

    Do you have any pictures of the current piping?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • VA_Bear
    VA_Bear Member Posts: 50
    I wonder...

    if the return piping has sagged or lost slope and is holding the water in the condensate return?
  • MDNLansing
    MDNLansing Member Posts: 297

    Have you removed the LWCO and tested the continuity of the unit when you move the actuator? If its installed at the proper level I's say it should cut the burner out when the glass empties. Personally, if I saw my glass empty and boiler still running, I'd check that right away.

    Also, if you using a pressutrol you might want to check the continuity of that too. Check for open and closed circuits when manually moving the bottom plates to actuate the plunger.

    Neither of these really address your issue, but they will prevent blowing up your unit while you figure it out.

    I can't see in the pics, but do you have a long wet return running low along the floor? If so, try to find a way to see if it has water in there when the boiler is idle. Then feel the pipe with the boiler hot. It should be filled with "cold" boiler water when off and "hot" boiler water when steaming. If that line empties when cold for some reason, then fills when hot it could certainly pull alot of water from the reservoir.
    ALIGA Member Posts: 194
    edited October 2013

    there is still plenty of water between the low point of the sight glass to the lower drain.

    the lwco does cut the boiler off, that has been tested.

    i used the wand, and also filled the boiler to the top with water, added tsp, and then drained. same behavior.


  • Rod
    Rod Posts: 2,067
    Slow Condensate Return

    Hi- I find that when you get “stumped” as to what the problem may be, it pays to go back and check out each item that might be causing the problem.  Don’t assume anything until you get a positive verification.        

    Things that can cause lack of boiler water:

    1.Water Quality- Since you have just flushed and skimmed, we can probably check this off.

    2. High Pressure- How do we know that the gauge is accurate? It might be an idea to check the pigtail and the port for obstruction and make sure they are clean. Do you have a second low pressure gauge?

    3. Partially Obstructed Wet Return - How long does it take for the water to return to the boiler after you shut down the burner? With no pressure, it should be fairly rapid. A slow return might mean the wet return is partially clogged up.  Being the lowest spot in the return piping,  Wet Returns tend to collect all the dirt and crud circulating through the system. I would open the wet return at the union and remove the nipple and elbow so I could visually inspect the inside of the horizontal part of the wet return.  I would also consider replacing the elbow with a plugged tee as that would make this inspection much easier in the future. (See attached picture)   

    In one of your other pictures of the Wet Return there is a sloped return pipe. (See attached photo)  Generally  the piping should be perpendicular where it drops down to the wet return and shouldn’t go horizontal until is higher than 28 inches perpendicular above the boiler’s waterline (The “A” Dimension)   Not being able to see how the sloped pipe is configured has me wondering whether this could contribute to your problem.  

    If you do find your wet return piping is clogged up, you may find it is less hassle, economically and labor  wise, to just replace it rather than clean it. Since it isn’t a steam bearing pipe, I replaced mine with copper piping and have been very happy with it.

    - Rod
  • Bio
    Bio Member Posts: 278

    Did you have the same problems prior the boiler change?
    ALIGA Member Posts: 194
    edited October 2013
    Bio - that is a very good question

    Unfortunately when I moved into the house, I did not pay close attention to the boiler. After one winter of service it died on me.

    After stumbing across heatinghelp.com and installing the new boiler, the boiler room has been like a man cave for me, and I have been paying closer attention to it.

    So to answer the question, I do not know if this behavior persisted with the old boiler.


    The gauge is 5 psi wika gauge installed last year. When the boiler shuts off, the water level comes back within less than a minute. As for the sloped return, it is about a 45 degree angle, roughly 5 feet in length.
  • Rod
    Rod Posts: 2,067
    Horizontal Return Height

    Hi- Are all the horizontal returns well above the “A” dimension (28 inch above the boiler’s waterline)?  The 28 inch height is approximately where the water will be backed up in the return lines at 2 PSI.  If water enters the horizontal return lines, either due to a lower return line or due to a higher than 2 PSI Pressure, this can account for a lot of “missing” water.

          As you can see, the sloped pipe uses a larger volume of water to reach the 28 inches than a vertical one would.  This is one reason it’s good practice to have your return lines to drop vertically down to the wet return.  The extra volume can’t be that much so I doubt that it is the major cause of your “missing” water.

    If the Return heights are satisfactory, I’d still think I’d bet on something being partially clogged up. Is your pigtail brass or steel?

    - Rod

  • Peteys
    Peteys Member Posts: 79

    Is the boiler flooding? If it is you might want to throttle back the feed valve so the condensate has time to return to the boiler
This discussion has been closed.