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Some radiators cool down as boiler fires? (with drawing)

I am a homeowner. In a previous post I foolishly said that I loved my steam heating system and that I had fixed it. This was too much hubris for the universe to stand, and so it broke. The funny thing is, it broke in a way that is very puzzling to me -- so puzzling that no one can figure out what is wrong, including two heating contractors.

Everything used to work, then one day I started having trouble with four out of my twenty radiators. They are all grouped in one area of my house. I made a sketch of the problem area here: <a href="http://bit.ly/4XMjGr">http://bit.ly/4XMjGr</a> (PDF scan of a drawing that I made)

Everything to the left of the drawing works.

Everything to the right of the drawing works.

Everything in the drawing used to work.

If I open the vent line near a problem radiator, that radiator will heat up as the air vents.

Important to know: Because I have an unusual heating system (the K-M-C Vacuum System: state of the art in 1906) there are no vents on my radiators. There is only one vent in the basement. This is what makes it a real puzzler to me. If the vent line were blocked, everything to the left should not work. But the fact that the stuff on the left works and the stuff on the right works means the vent line must be working OK, at least in the basement.

Two of the radiators warm up a little at the middle of the heating cycle (I labeled them #2 and #3), right when I would expect them to. Then they cool down. They cool down while the boiler continues to fire and well before the system shuts off. So the boiler is steaming but the steam is not going here for some reason. But the fact that they DID get warm at all means that the steam CAN get there and the venting does work briefly.

I'm really not sure what to do. This is a major problem as 4/20 radiators not heating means a big part of my house is suddenly not livable! My impulse is to add venting but I'm not sure where. Any ideas?

Here is a flickr photoset of my radiators in case this helps: <a href="http://bit.ly/52DibN">http://bit.ly/52DibN</a>

I bought Dan's books and read them. I have the patents and documentation for my system. I'm still not sure what to do and my contractor doesn't know either. I really, really appreciate any thoughts you might have on this! Please!


  • nicholas bonham-carter
    KMC problems

    i assume your pressure continues to be low [a few ounces], and so must imagine that the air is not getting out of the cold radiators. can you open the vents on the individual  cold radiators, and feel steam rising?

    if that works, then most likely, there is a blockage in the air vent line some where which would affect the "cold group". probably, the line will have to be blown out with air, or water pressure.--nbc
  • chgosteam
    chgosteam Member Posts: 3
    air line return

    Your problem lies in the air line return traps or "vents"  Although your gauge says KCM this system looks like it might have been retrofitted to a Dunham air line reurn system.  It used vents like yours.  They functioned like crossover traps in a 2 pipe system.  Most times the air line was induced in a vacuum either mechanically or naturally.  Your system is now neither.  It is basically working like a fancy one pipe steam system.  One problem.  When those "vents" go bad and pass steam they will lock the air in other radiators.  This will cause the radiaitors to stop heating early in the cycle or not heat at all.  With steam pressure on both sides of that trap, or "vent" the air will stay put.  Replace those air line return traps with radiator vents of your choice and cap that air retrun at each radiator for now.  You should check each radiator air return line also to see which ones are passing steam, they will be hot after the "vent" replace those as well. 

    Meanwhile you should look into converting this to a standard one pipe system.  Make sure all those mains are properly vented and the pressure is kept below 2 psig.  Replace the radiator vents and vent them according to thier size.
  • niftyc_2
    niftyc_2 Member Posts: 34
    So are all systems with air return lines eventually doomed to be converted to air vents?

    Thank you so much for the fast replies!

    Nicholas: you never know what those pipes are doing in the walls, but it looks like there couldn't be a blockage that would affect all of those radiators! You would need at least two blockages, right? That's why I did the drawing. It is a puzzle. However, I took the air lines apart at each radiator and tried blowing into them with a shop vac -- no result.

    chgosteam: I like your theory best but I can't find a radiator is hot on the return side. The air return lines are not warm. The radiators have been retrofitted with F&T traps on the air return side to prevent this problem but I can't find any failed traps. I also tried closing the supply valves to nearby radiators (they still work) in case I just missed the failed trap but this also doesn't affect the problem. Mysterious!

    I agree it's fancy one-pipe but with no way to balance the system since there is nothing to adjust on each radiator. So it seems like for now I should cap the return lines and vent the 4 problem radiators? The rest of the system works and I am hesitant to modify any more than the radiators that aren't working. I guess the F&T trap route that previous owners have taken is a much more expensive version of your proposed retrofit.

    What is your favorite vent?
  • niftyc_2
    niftyc_2 Member Posts: 34
    answers to questions

    Oh and I forgot to answer: Yes I have the pressure low. Currently the only vents are at the end of the air return pipe system. I added these. When I bought the house the system had no working vents at all -- I'm not sure what it was like to live in the house in winter!

    There are no vents on the steam mains right now. I know I should do this and I raised this point with one contractor and he said that drilling into the old iron mains was worrisome as they are brittle and you never know what will happen. Maybe I should overrule him or find another contractor?
  • BobC
    BobC Member Posts: 5,479
    What changed

    If it worked before and now doesn't, something has changed and we have to figure out what changed. It's been a long winter and I've noticed everything is looser because the wood has dried out more than usual.

    Has anything been done that might have changed the slope of the piping? I have a radiator that stopped heating fully at one point while everything else was fine. I noticed the vent on that radiator was panting some and thought I might have water lying in a horizontal pipe somewhere. There is a short horizontal pipe on the second floor that I suspected so I raised the whole radiator up 3/4" and that solved the problem.  Old houses settle over time and what was once may no longer be so. Yours is a two pipe system but pooling water will still cause problems, go over any horizontal pipes you can reach and make sure the slopes are correct and there aren't any dips.

    Do you have a low pressure gauge so you can reliably see what the system pressure is doing during the steaming cycle, is there any dip during the cycle that might yield a clue?
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge