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McDonnell miller 47-2 overfilling boiler

I have a McDonnell & Miller 47-2 autofill unit on my steam boiler system.
The system was leaking water into the boiler when the furnace was off. I have since replaced the valve and strainer assembly. The water level remains rock solid on its set point while the furnace is off. When I run the furnace the level holds steady for a while, then near the end of the cycle it overfills the boiler. I took the float body apart and removed the sediment from the lower bowl and scrapped of the heavy rust deposits. I cleaned the top as best I could; and would have cleaned it more thoroughly if I could have figure out how to remove the float assembly. I put it all back together and the problem is still there. At my wits end, any advice would be appreciated.
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Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,955
    Step one here is to be really sure that the float drops when the level is low -- and then comes back up and opens the switch to fhe feeder when the level rises. If it's not doing that, you need to clean the float and float chamber again, and check that the switch is working correctly.

    Now. What kind of automatic feeder is the low water cutoff controlling? Many of them have provisions for regulating the delay between a call for water and the valve opening. This is to prevent just what you are experiencing, which is due to slow return flow. Is there such a provision on your feeder?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • 109A_5
    109A_5 Member Posts: 1,346
    Hello @matt_mccracken123,
    Are you loosing too much water from the boiler due to clogged up returns ? So the water stays out in the system too long and the feeder thinks the boiler is low, so it fills it, then when the boiler shuts down and the condensate slowly returns back to the boiler, the boiler becomes flooded.

    Or does the fill procedure just not shut off when it should ?

    Looks like M & M 47-2 comes apart easily enough with the correct tools. May need to buy or make gaskets upon reassembly.



    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    kcopp
  • jringel
    jringel Member Posts: 27
    If it's only happening at the end of the run i would check the returns as they are most likely at least partially clogged
    John Ringel Energy Kinetics
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @Jamie Hall the float appears to be working correctly. There is no delay, when the float drops water is added to the boiler. I did clean the float bowl, I was able to get the bottom pretty clean but I wasn't sure how to remove the float, so I cleaned it the best I could with the float in place.
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @jringel, Thanks, I'll check the returns, it is an old steam system.
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @109A_5 Thanks I'll check the return. It makes sense because it only floods after a long run, like first thing in the morning. I had actually thought about installing a solenoid valve with a delay to allow time for condensation back to the boiler.
  • tim smith
    tim smith Member Posts: 2,743
    Other item, do you dose chemicals either manually or feed pump? I have ran in to issues with high chemical levels causing the water level to drive down on long run and adding water when really does not need any. Then shuts off and boiler flooded. If chemical in question, dump boiler and refill with fresh water.
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @tim smith, no chemicals added.
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @109A_5 Actually the system is a single pipe system, would a chemical flush be a better alternative then trying to clean the lines?
  • delcrossv
    delcrossv Member Posts: 688
    edited February 6
    If it's single pipe, probably lack of pitch is the problem. A timed delay (like what Hydrolevel provides in the box) is a good solution. Just make sure you wire it so the burner stays off until the condensate gets back. ;)

    I had the same problem in one of the buildings but just set the VXT to 10 minutes and solved it
    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
    Long Beach Ed
  • 109A_5
    109A_5 Member Posts: 1,346
    edited February 7
    Hello @matt_mccracken123,
    A timer like this may help (24 VAC system), but it would be much better to get the returns running correctly. It won't get better by itself, only worse, and may cause other issues.

    https://www.supplyhouse.com/ICM-Controls-ICM203FB-ICM203F-Delay-on-Break-Timer-6-Wire-Leads-03-10-Minute-Knob-Adjust-Delay

    This file may help you understand how the M & M 47-2 comes apart. Exploded diagram and parts list.
    https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1350568975981/83565_PROD_FILE.pdf

    I'd try to flush it out with a garden hose type thing if there is some kind of service ports available. Don't let the pressure go too high or you may be replacing old pipes.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @1095A_5, very helpful. I had the float bowl apart but couldn't figure out how to get the bellows assembly apart. looking at the diagram, I'm not quite sure what holds the arm in place. I think at this point when I had it all apart, the rust may have been holding it. I will try to do something with the lines, I was thinking a chemical flush. it's a big house, lots of pipes, too much to take apart and clean. The switch seems like a good temp fix for the problem. Would that be used in conjunction with a solenoid water valve? Would the valve be normally open or normally closed?
  • 109A_5
    109A_5 Member Posts: 1,346
    Hello @matt_mccracken123,
    I actually took a second look at that fill valve assembly. I thought it was electrical, however it looks like it is just mechanical. So the timer idea will not work like I thought it would.

    A timer would work but it would have to limit the boiler running duration and may be awkward. I was originally just thinking of just delaying the fill electrically long enough for the condensate to return.

    I would say once this housing is removed (Red) and maybe a gasket (item 6) that holds the arm and the pivot assembly to the upper float housing. Also looks like there may be a nut retaining the float to the arm. Looks like it may be awkward to do with it on the boiler. Build up of crud in the bellows may restrict the movement of the bellows. Carefully clean so you don't damage the bellows.



    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Long Beach Ed
    Long Beach Ed Member Posts: 1,188
    You can use a screwdriver through the window in the housing to manually operate the float arm. That will tell you if it's hanging up. I doubt it is. These things are generally bullet-proof. A beautifully designed tried-and-true device.

    As folks here have suggested, you have to look outside of the boiler room. See if there's a way of getting a hose attached to the returns and flushing the crud out of them with some line pressure. Your problem is likely slow returning condensate.
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @A1095_5 Now I'm not sure that I really understand what's going on. I was checking on the boiler tonight and noticed the water level was high. That made sense because the furnace had just run. I left the water feed line valve open and proceeded to drain off the excess water, before the water was to the high fill line the auto fill was adding water. when I closed the petcock the water level went to the top of the sight glass. After that I shut the water off and drained the boiler to the bottom of the sight glass, then I turned the water back on, it filled to the normal fill level. Does it sound more like a malfunctioning float, perhaps due to the build up that I wasn't able to clean above the bellows? I took a video, but the site won't upload videos.
  • Long Beach Ed
    Long Beach Ed Member Posts: 1,188
    edited February 8
    Is the #67 piped correctly? Remember that this is a safety control and should be piped specifically as instructed in the literature. It must be installed to feed only to the critical lowest water level. The water line cast in the float housing should be near the bottom of the sight glass (at the lowest permissible water level).

    Some installers try to make it a convenience control and set it up to feed water up to the "normal" water level of the boiler. Naturally, in that case, it feeds when the boiler steams only to be overfilled when the condensate returns from the radiators.

    If it is piped at the correct level, make certain that the pipe connections are correct and that the water flows freely between the float chamber and the boiler with no intervening valves, mud or mung .
    exqheat
  • 109A_5
    109A_5 Member Posts: 1,346
    Hello @matt_mccracken123,
    If you are confident that the Low Water Cut Off (LWCO) function works 100% correctly, I think what I would do is; Shut off the boiler for a while so if there is a slow wet return most of the condensate can return to the boiler. Fill or drain the boiler to the normal water level, shut off the water feed supply valve. Turn the boiler back on and watch its operation for a few cycles or enough you understand things better.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    delcrossvkcoppexqheat
  • 109A_5
    109A_5 Member Posts: 1,346
    Hello @matt_mccracken123,
    BTW with videos, typically folks post them on their favorite web hosting site that hosts videos and then post the link to the video here.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • pedmec
    pedmec Member Posts: 942
    bit of advice? change it before you flood your system and risk flooding your house. the linkages sometimes will get hung up and then it will never shut off. i say this because i don't think it's a good idea to keep playing around with that style of low water cutoff because its also feeding your boiler. The property manager i work for had one flood a six story condo 48 unit condo because the oil company kept trying to repair it. if you can't see it right away then the more times you play with it the more chances of having some catastrophic go wrong. that's just my take from experience.
    exqheat
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @109A_5 here is a youtube link to a video made last night. https://youtube.com/shorts/JrEqR0Dj_Zs?feature=share
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @109A_5 here is a second youtube video made last night. https://youtube.com/shorts/RKLVYfZVwI0
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606
    edited February 8
    When you use the blow down valve at the bottom of the #47 you are also allowing the float to drop as the water leaves the bottom of the float chamber. Since that float lever is connected to the #2 switch to stop the burner AND the lever that operates the fill valve. That valves MUST open as a result of draining the boiler at that blow down valve. So what you are describing and showing is normal.

    On your WM SGO boiler there is a drain valve at the bottom of the boiler. If you use that valve the drain the excess water, the issue you described in your first video will not happen because that blow down valve will stay closed when you are draining the boiler thru a different valve.

    Now to be clear about your problem. This overfilling has not been a problem from the beginning when the WM SGO was installed... is that correct? This is a new situation that has started after years of normal operation... is that also true?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @EdTheHeaterMan The overfilling has been a problem for a while now. I replaced the valve because it was leaking water into the boiler gradually over time. After replacing the valve, that is no longer the problem. However after a long run in the morning, about 1 1/2 hrs. it overfills. It is less likely to overfill after shorter runs.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606
    edited February 8

    @EdTheHeaterMan The overfilling has been a problem for a while now. I replaced the valve because it was leaking water into the boiler gradually over time. After replacing the valve, that is no longer the problem. However after a long run in the morning, about 1 1/2 hrs. it overfills. It is less likely to overfill after shorter runs.

    CLOSE, But not the full answer to my question... Has there ever been a time what your SGO did not have this problem?

    The reason for asking is that I do not believe the M&M 47-2 has anything to do with your problem. I believe that it is working as it is designed. So if there was a time that you did not experience this problem, then the system piping (probably the return) is not letting the condensation back into the boiler as fast as it used to.

    If however the problem existed since the SGO boiler was installed, then there is a design flaw with the system. Perhaps that M&M 47-2 is not the correct LWCO and water feed for your system. The WM SGO most likely replaces a boiler that had a higher water line and had a larger water content. That may be part of the problem if the problem was always there from the start of the WM SGO.

    So has this boiler ever operated without the problem you described?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    Long Beach Edjringel
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    I bought the house about 17 years ago. The M&M 47-2 was operational and had no issues. About 10 years ago, it started giving me problems overfilling, to resolve the issue, I shut down the autofill and started to fill it manually. recently I started working on the M&M 47-20 to see if I could get it operational once again. I've changed the valve as I said and cleaned the float bowl as best as I can. The float appears to move freely
    without obstruction. I was wondering about the return, it's a large house an lot of pipes, would a chemical flush work to clean some of the build up out of the pipes?
  • Jamie Hall
    Jamie Hall Member Posts: 22,955
    The first step is to flush all the wet returns (no need to flush dry returns or mains). This may be easier said than done, depending on how they are arranged and what access you have to them -- at both ends of each of them. You don't need a chemical, however. What you need is a hose and a drain...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @Jamie Hall this is a single pipe system, are there wet and dry returns?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606
    Chemicals can help. But 17 years of mud in the returns will take more time for chemicals to do the job.

    Is there a valve or a union on the return pipe that is below the water line (Wet Return). If you have mostly Dry Returns then those pipes may have steam in them and only a small amount of water at the bottom 1/4 of the pipe that is constantly moving. So those pipes are clean. (Steam cleaned) Once you get the water to collect below the water line, (in a wet return) that is where the suspended solids in the water will settle to the bottom of the return pipe(s). Over the 17 years, those pipes below the waterline will have a substantial amount of mud to be removed. The best way is to get water to flow quickly across the mud. Think of it like cleaning your sidewalk or driveway with a garden hose. The water pressure is going to move the dirt based on the water pressure applied.

    If you just let the chemicals sit there and work on the dirt, (in your pipes or on your pavement) it may take some time to move that mud. Then you will need to wash that chemical and mud away with the hose anyway. See if the hose will do the job without chemicals. You will be making a mess on the floor where the pipes are, unless you can get a opening on the one end of the pipe to put the water pressure in and a opening on the other end of the pipe to connect a drain hose and place the other end of the drain hose someplace where all that mud will not make a difference.

    The water pressure in that wet return that is moving that water under normal operation is less than 5 gallons per hour, the water pressure in a garden hose will be moving 5 gallons per minute. That will move some serious mud out of that pipe.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @EdTheHeaterMan ,
    Attached is the side view of my boiler. Fill level is a little more than half way. There is a cast iron pipe on the left that branches into a copper pipe on the right. Looks like the cast iron pipe has an axis port.
  • delcrossv
    delcrossv Member Posts: 688
    Oh boy.
    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606
    edited February 9


    Lets assume that this worked at some point. The wet returns are the pipes that are connected to the bottom of the boiler that come from the end of the supply main if it is sloped away from the boiler. basically the blue arrow in the correct illustration, and those pipes can be very long, from the other side of the basement.

    If you have a one pipe counterflow system, then the returns are shorter.

    I believe that you may need someone familiar with steam boilers to go over your situation. There are some issues.

    Edit: i added a file below so you can zoom in on the illustration
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    delcrossv
  • 109A_5
    109A_5 Member Posts: 1,346
    Hello @matt_mccracken123,
    The water level raises quickly due to the flow characteristics of the LWCO and the sight glass to the boiler assembly.

    You may find this video interesting. There are others too.
    So this is what obsolescence looks like....McDonald-Miller 47-2 LWCO
    https://youtu.be/bBB4G_-5_pg
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606
    To make this more complicated, someone added a water filled radiator loop to the system, just to make it more difficult to figure out. You really need someone with knowledge of steam boilers on location, to help you out.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606
    edited February 9
    109A_5 said:

    Hello @matt_mccracken123,
    The water level raises quickly due to the flow characteristics of the LWCO and the sight glass to the boiler assembly.

    You may find this video interesting. There are others too.
    So this is what obsolescence looks like....McDonald-Miller 47-2 LWCO
    https://youtu.be/bBB4G_-5_pg

    I disagree. The M&M 47-2 is a great LWCO with a built in water feeder. You can still specify that as your primary LWCO on just about any residential boiler. I happen to prefer the float type LWCO over the probe type. The Float type is able to be flushed weekly to keep the float path free of debris and build up. The probe type must be removed from the boiler to clean the probe and that ain't happening once a week. These guys seem to like the float type LWCO. https://www.youtube.com/watch?v=7tvdOVN_aqk
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    GordoLong Beach Ed
  • 109A_5
    109A_5 Member Posts: 1,346
    Hello @EdTheHeaterMan,
    The video is @Gordo's opinion. I don't have a problem with the M&M 47-2. I thought @matt_mccracken123 may like the cutaway view that @Gordo shows near the end of the video. Since @matt_mccracken123 could not fully disassemble his M&M 47-2 for cleaning.

    I like my M&M 67, easy to maintain and no electronic goofiness or failures. And I manually feed the water, not a problem.


    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    EdTheHeaterManGordoLong Beach Ed
  • matt_mccracken123
    matt_mccracken123 Member Posts: 39
    @EdTheHeaterMan "To make this more complicated, someone added a water filled radiator loop to the system, just to make it more difficult to figure out."
    I thought you might notice that, it was that way when I bought the house. The boiler guy I have sat there staring at it for some time, then says to me he's never seen anyone hook a closed water system into a steam boiler system. The guy that owned the house before me owned an oil delivery and service company, it might explain the few oddities with the system. when I get home tonight I'll take another picture so you can see what was blocked by the insulation.
  • Jamie Hall
    Jamie Hall Member Posts: 22,955
    Your boiler guy may never have seen a closed hot water loop on a steam boiler, but it's actually not that uncommon. Does not inspire confidence...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    matt_mccracken123Long Beach EdWaher
  • Mustangman
    Mustangman Member Posts: 16
    The Hydrolevel VTX 24V or 120V work incredibly well. They have all these delay times to choose from. Not getting condensate back to the boiler in time to prevent overfilling is a common problem. When the VTX senses the water is low, it will delay the refill cycle to what ever delay you program in. If this is a relativily new issue, you have to ask yourself what would cause that? The list can be long. Traps that are not working, an obstruction in the return. A good place to look for a blocked return is if it you return is piped around a door way.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606

    The Hydrolevel VTX 24V or 120V work incredibly well. They have all these delay times to choose from. Not getting condensate back to the boiler in time to prevent overfilling is a common problem. When the VTX senses the water is low, it will delay the refill cycle to what ever delay you program in. If this is a relativily new issue, you have to ask yourself what would cause that? The list can be long. Traps that are not working, an obstruction in the return. A good place to look for a blocked return is if it you return is piped around a door way.

    The float is connected to a #2 switch. That switch only has 3 terminals. Com. NO and NC. To wire that up to the Hydrolevel VXT 120 the burner power would need to go to the com and the burner would go to the NC. When the burner lost power as a result of low water, the VXT would then get the burner power to feed water. The time delay would then not allow water feed to open "Hoping" for some slow moving condensate to find its way back to the boiler. Then the burner could restart without the feeder adding water. This would be good as long as the clogged pipe does not clog anymore.

    It seams that the system operated properly before the return pipe(s) got clogged. By redesigning the return to include some easy way to do maintenance to include flushing the wet returns from time to time might be a better solution., because that is going to be needed anyway.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,606
    The guy that owned the house before me owned an oil delivery and service company, it might explain the few oddities with the system. when I get home tonight I'll take another picture so you can see what was blocked by the insulation.


    Does that oil company still exist?
    Are you purchasing your oil from that company?
    Does that company (or your current oil dealer) have a good steam man?

    Side note: The previous owner's oil company had a steam guy that was not that good based on the way the boiler is installed. But that guy may have learned something in the past 17 years. He knew enough to add a wet radiator loop.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics