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Sealant For Steam Radiator Fill Nipple Without Disassembly ?

SteamHeat Member Posts: 159
One of my radiators has developed a small leak where the steam enters.

It appears to be coming from the close nipple between the radiator and the fill valve, right where the nipple meets the radiator.

It is a 78 year old connection, so I am not sure if my pro even with the best tools and techniques could disassemble it.

Is there some brush-on sealant, maybe a Loctite or Permatex product, that I could use to paint on the area where the nipple meets the radiator, to seal the leak until summertime and then try a more permanent repair or replace the whole radiator ?


  • Jamie Hall
    Jamie Hall Member Posts: 21,573
    Permatex or high temp RTV might work, if you get the surfaces really really clean. Since you are going to be trying to get the spud out, I can't recommend JB Weld...

    With some careful work, you will be able to get the spud out of there and clean up the threads. You may not be able to save it, though, so before you begin get yourself a new steam valve and matching spud to reinstall.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • acwagner
    acwagner Member Posts: 505
    I've used RTV silicone with good results in a similar situation on my own system. It's generally available at hardware stores in the automotive section.

    As @Jamie Hall said, it's all in the preparation just like painting. You need to remove all the rust and paint and try to get to bare metal around the leak. The surface also needs to be dry, which can be a challenge in your situation since it's currently leaking. You'll want to isolate that radiator if you can and let it cool down before doing all this. And, after you apply the silicone, give it several hours (at least) for it to cure before letting steam back in that radiator.

    Might be worth having a pro come out and look at it anyways. You'd be surprised--the permanent fix might be easier than the temporary fix. Most pros have various tricks of the trade to remove old fittings, so it might not be as difficult of a job as you think.
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  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,575
    Often a leak from the union nut between the inlet valve, and the spud can look like a thread leak, when in fact it is just an imperfect mating of the union surfaces. Retightening it should stop it.
    Keeping your pressure low will help as well.
    The dead men would use lead wool pounded into a threaded joint to stop the leaks.—NBC
  • SteamHeat
    SteamHeat Member Posts: 159
    Thanks guys.

    Could any of you suggest a particular Permatex formula? Many of the Permatex thread sealants seem to be described as also being thread lockers and I don't want to make it even harder for my pro to remove the spud in the summertime. There are also many different Permatex RTV's too. Since this is an "off label" use, the product descriptions are not very helpful in deciding which to try. If anyone could give some guidance I would really appreciate it.


    Permatex lists these as thread sealants:
    56521 High Performance Thread Sealant, 59214 High Temperature Thread Sealant, 54540 Pneumatic & Hydraulic Sealant, 80631 Thread Sealant With PTFE, and 57535 Seal & Lock


    Permatex lists these as gasket RTV's:
    81879 Ultra Copper, 81727 Ultra Blue, 82181 Ultra Black, 22072 Ultra Black Advanced Formula, 22071 Water Pump & Thermostat Gasket Maker, 81160 Red, 80050 Clear, 80022 Blue, 81182 Gear Oil resistant.
  • Jamie Hall
    Jamie Hall Member Posts: 21,573
    I've always just sort of punted and used the red... but it's what I have around.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SteamHeat
    SteamHeat Member Posts: 159
    Jamie, thank you. I'll try the Red 81160.

    I run at a maximum pressure of 16oz. So I am hoping that it will hold if I can get it into the right spot. I am pretty sure it is the radiator side. I will find out for certain once I smear the stuff on and it cures.

    Also, using the RTV should be easier than finding a Lead Sheep nowadays.
    I wonder how they used to shave the Lead Wool off of them? :) LOL!
  • Pumpguy
    Pumpguy Member Posts: 612
    edited January 2018
    You might want to take a look at Loctite's #290 wicking grade sealant. In addition to sealing and locking threaded connections after assembly, it is recommended for sealing porous castings.

    See attached file for more information.
    Dennis Pataki. Former Service Manager and Heating Pump Product Manager for Nash Engineering Company. Phone: 1-888 853 9963
    Website: www.nashjenningspumps.com

    The first step in solving any problem is TO IDENTIFY THE PROBLEM.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,085
    Hello, A trick I've used in the past is to impregnate string with silicon, Do this by wearing gloves and putting a glob of silicon in one hand and pulling string through that glob and through fingers. Wrap the gooey string around the cleaned up and dry joint. Let set, and you now have a fiber reinforced gasket that can take some pressure. B)

    Yours, Larry
  • SteamHeat
    SteamHeat Member Posts: 159
    Thanks guys.

    I will try the string trick with the Permatex Red RTV.
    If it does not hold, then I will try the Loctite 290.

    I am a little worried that the Loctite 290 might work better as a locker than a sealant, but if the RTV doesn't work I will try it.
  • diamond67
    diamond67 Member Posts: 9
    This is a very timely thread. I have an old (1830) farm house with steam heat that's obviously not original but I'm pretty sure it's older than I am (vintage 1967).

    We're planning (hoping) to rip out the whole heating system this summer but I just noticed we have a leak again. We had it a bit last year and now it's back with a bit of a vengeance. It's right at the coupling into the radiator which I assume is the spud. (Obviously not a pro here!)

    Someone mentioned using JB Weld and that you wouldn't want to use it if you're later going to try to get the pieces apart. What about if you're just looking for a temporary fix and will eventually be trashing the whole system? This is a weekend house so the system doesn't run full blast very often. But it is in a cold climate (Catskills) so I do need it to function.

    Are there any tricks to using JB Weld? The stuff seems a bit too good to be true.

  • SteamHeat
    SteamHeat Member Posts: 159
    edited January 2018
    Dear Diamond67,

    I'm the original poster.

    I went to the local autoparts store to buy a tube of RTV and after looking at the ingredients, I decided to use the Loctite instead. I am waiting for it to come in the mail.

    Under the hood of a car if any of the many heavy chemicals in a tube of RTV outgasses, it is not a big deal. In someone's bedroom, it might be significantly less desireable.

    I have not used JB Weld myself, but I have seen it recommended in many places for steam radiator fixes.

    I hope you are replacing old steam system components with newer ones and not switching to hydronic. I had hot water heat in one residence and steam in two others and I would say that I would rather have steam where I reside over any other type of heat. It may not be quite as numerically efficient, but there is nothing like the heat rolling off a 215 degree hot radiator to warm your home and your bones. It is just a really good feeling.

    Good luck with your repair and whatever system you have next.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,575
    The leak could be from the union nut, which can be tightened up and sealed.
    I expect if you listed the problems you have had, which makes you want to “trash” the old system, and then followed the advice here, you would keep the old system.Steam is very good with long term setbacks, and so when you arrive at your country house, and dial up the heat, it does not take long to recover.
    Good luck, and keep the old radiators in the shed, so you can always reinstall them later!—NBC
  • KC_Jones
    KC_Jones Member Posts: 5,435
    diamond67 said:

    We're planning (hoping) to rip out the whole heating system this summer

    Why on earth would you do that? Seriously what are you hoping to gain or improve?

    I hope you aren't talking about doing forced hot error?!
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  • HomerJSmith
    HomerJSmith Member Posts: 2,276
    Using JB-Weld on a dry clean surface, I would think is your best bet as it is a topical application and when cured provides strong resistance against pressure. As it is topical, it is easily removed and would not impede removal of the nipple later on.

    There are on YouTube videos of how to remove nipples and spuds from old cast iron radiators. Over the years these are pretty much locked in and can't be extracted by unscrewing.