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Water level with autofeed

We have an old steam boiler that is mostly working fine. For a long time, however, the water level has been 2" or 3" above the "normal" water level indicated on the side of the boiler.

I think I have finally figured out that the automatic feeder was mounted too high. The main connections have some "extra" pipe nipples that are 2.5" long. See picture below. This happened before we moved in and has caused no obvious problems in at least 10 years.

As part of the investigation, I read the McDonnell & Miller manual for the feeder. The manual suggests to disassemble and clean the feeder every year and to replace it every ten years. The feeder is more than 10 years old and has not been disassembled and cleaned, as far as I know.

I blow down the feeder once a week during the heating season and there are no obvious problems with the feeder.


1. Should I disassemble and clean the feeder?
2. Should I replace the feeder preemptively?
3. While doing either one, should I lower the feeder 2 or 3 inches by replacing the pipe nipples with shorter versions? (This also requires re-piping the nearby water lines.)

I am not inclined to do anything during the heating season. But does it make sense to do any of the above during the summer?

I am concerned that someone intentionally mounted the feeder a little high to correct some other issue I have not discovered. However, I suspect that the person mounting the feeder mistook the line cast into the feeder as an indication of the water level. The manual says to mount the feeder so the line is 2" or 3" above the minimum water level. If I do that, the actual water level will end up at the "normal" line on the side of the boiler.

Thank you,



  • Jamie Hall
    Jamie Hall Member Posts: 23,324
    The line on the side of the float chamber is the level it will trigger at, and that, so far as I can see, is pretty close to the normal water level marked on the boiler. So... it's mounted pretty close to correctly as it is.

    So that takes care of your 2 and 3 Don't bother. 1 is another matter -- it may not be a bad idea. However, be sure you have all the necessary replacement parts and gaskets on hand -- gaskets particularly. Don't try to reuse old gaskets.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • LudgerHentschel
    LudgerHentschel Member Posts: 22
    I apologize if I used the wrong terminology.

    Per the online manual, the "big, black ball" is both the low water cut off and automatic feeder. It seems to provide both functions on my boiler.

    The manufacturer sells several units that look very similar to each other but provide different combinations of low water cut off and automatic feed.
  • Lance
    Lance Member Posts: 270
    McDonnell Miller 47-2 feeder with a low water cutoff #2 switch. Just like a float ball in a toilet but for steam. Steaming is a process governed by speed. Speed to boil and condensate, speed to distribute, speed of water return and enough speed to refill but not too fast. I like to install a pressure reducing control on my water feed pipe to insure a steady slower rate of feed that helps maintain a more stable water level hopefully. Feeding a 1/2" pipe at 60-80 PSI is too fast a rate. I feed at 12 PSI. Often this prevents steam pressure drop due to cycling which creates other issues. While this install height of the feeder may not be bad, lowering may also work, the reason I would lower this is if during the off cycle, the boiler floods too high. PS. Insurance companies and inspectors like to see the bowl off and the inside of this feeder cleaned before they allow a commercial boiler back in operation. Sludge can prevent the float to drop and allow a boiler to dry fire. I am more concerned about the steam riser pipe height off the boiler as being a little short.
  • neilc
    neilc Member Posts: 2,703
    somebody got creative with the piping to the LWCO/feeder,
    notice the 2 extra 90s top and bottom, and the 2~3 inch nipples betweenst them?
    there's you water level discrepancy.

    what does the header look like ? picture ?
    known to beat dead horses
  • LudgerHentschel
    LudgerHentschel Member Posts: 22
    The header is wrapped in insulation. I will look for a picture.