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leak at radiator pipe union


I live in a three storey walk-up condominium building with steam heat. The system is as old as the building - about 90 years. The system is a little quirky, but generally works really well.

One of my radiators has a leak at the packing nut and at the pipe union. Can anyone provide step-by-step instructions on how to repair both leaks? My instinct is to take a pipe wrench and try to tighten the nuts, but I'm a little worried about the possibility of breaking the cast iron.


  • BobC
    BobC Member Posts: 5,401

    Was this radiator recently moved or disconnected? Is the heat just now coming on for this season? I'm asking just because it's unusual for them to start leaking at 2 points spontaneously.

    Try tightening that top bonnet nut with a wrench, if that doesn't work buy some valve packing at the hardware store. When the system is off unscrew that bonnet nut and wind the valve packing around the stem clockwise (the shaft the knob goes on) and tighten the bonnet nut down over it.

    Next try tightening the large coupling nut with a pipe wrench and see if that works. Don't try using a pipe on the end of the wrench or a hammer. If that nut breaks you will be in  trouble and you may have to call a plumber.

    The valve and the spud that screws into the radiator are a matched set. To replace them the steam will have to be off to that whole area of the building, if not the whole building while you replace them. You will have to get the spud out of the radiator (a tough job) and you install a new valve and spud assembly - make sure you get the right size. All of that is not something you want to be doing if you don't have a day or two and some serious mechanical know how.

    If tightening doesn't work you could try loosening that nut all the way and putting some pipe joint compound on the face of the convex mating surface to fill any tine voids. that radiator is very heavy, slide some thing slick under the radiator feet (cut up pieces of milk jug) so you can slide that radiator on the floor if you have to.

    good luck,

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Sil
    Sil Member Posts: 72
    While I am Not a Pro

    These should both be fairly easy fixes.

    This video shows how to fix the valve stem:


    As for the union, you could either try to tighten it, or i would remove the union, apply pipe dope and re-tighten.
  • will smith_4
    will smith_4 Member Posts: 259
    And then again...

    If all else fails, get yourself a new valve and a spud wrench, shut down the system and replace the shut-off. A spud wrench will allow you to remove the fitting that inserts into the radiator, and then install the new shutoff. 
  • Sil
    Sil Member Posts: 72
    edited November 2010
    Spud Removals Rarely Go Easy

    Be advised that removing the spud may not go smoothly. That valve has been in place for 80 years (paint and rust). If you do go the spud route, make sure its a day you can live without heat for a while and have a back up plan (like a plumber on call).

    I'd wait for the sping to do this - unless the leak is significant.
  • noremac
    noremac Member Posts: 7
    good questions

    Bob: I don't know the answers to your questions, as I've only lived in this place a short time.  I'm guessing it was moved recently, as the floors have been refinished.  They have leaked right from when the boiler first went on in the fall.

    I don't think I'm willing to risk replacing the spud, but I think I can tackle putting some pipe dope on the mating surface.  Fixing the packing nut leak seems straightforward enough.

  • BobC
    BobC Member Posts: 5,401
    good choice

    I agree that repacking the stem and putting pipe dope on the mating surfaces is the way to go. If it was a single familly home you could go further but you can't control the building while you try taking spuds out of radiators.

    good luck,

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Jamie Hall
    Jamie Hall Member Posts: 21,111
    Go easy

    on that spud union.  First off, make sure that you are turning it the right way!  If it has been moved recently, it should loosen fairly easily -- get a wrench on it (24" should be ample) and see if you can loosen it just a little.  Then this is important: the mating faces of the union must be properly aligned; you can NOT torque the nut tightly enough to pull the faces into alignment.  You may have to lever up slightly on the riser to get the faces lined up properly, or shift the radiator slightly to one side or the other.  Then, while you are tightening the union nut, it may help to rock the radiator (gently!) from side to side as you turn it.  Tighten it up and see if you can get it that way.

    If that fails, you loosen the nut completely and pull the mating faces of the union apart (not quite as easy as it sounds).  Make sure that the mating faces are really truly clean -- no grit or crud on them anywhere.  You could use a little thread dope on it -- make sure it goes all the way around smoothly, and thin -- although I've never had to do that (yet) -- and try again.  With the nut fully loose, too, you can see what the misalignment is and be better able to correct it.

    Unless the faces of the union are seriously damaged, you shouldn't have to replace the spud.  That almost never goes easily...

    The packing around the valve stem shouldn't be a problem.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
This discussion has been closed.