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Best Boiler Stop-Leak (Boiler Leak Sealer)

MrVince Member Posts: 8
Happy Thanksgiving, everyone.

I've got a boiler that needs some attention. There seems to be a small leak coming from one of the sections. But, with contractors' hectic schedules right now, we'll need to replace it in the spring or at least 2 months from now.

Can you guys, recommend the best boiler sealer?

There seems to be several products on the market:

- Hercules Boiler Stop Leak
- Gunk's Liquid Boiler Sealer
- Black Sawn's Boiler Stop Leak
- Safe's Silver King
- Hydro-Seal Boiler Stop Leak
- Utility's Boiler Weld

Which products have you, guys used and how were the results? Each of these products come in liquid or powder form. Did you find that the powder form was more effective?

By the way, this forum is a great place for people to help each other. Thanks for the help!



  • nicholas bonham-carter
    Can you describe the nature of the leak? Is it a pinhole in the metal, or perhaps a bad gasket between the sections?
    My experience with stop leak shows it can slow a leak down, but probably not stop it. If you had a hot water system, you would have better luck in stopping this. Some of the products are so smelly as to drive the occupants out of the building for a couple of days.
    Make sure your pressure is reduced to mere ounces, with generous main venting, so as not to put any pressure on the leak.
    You probably only have a couple of weeks before this lets go, so plan on the replacement now, by figuring out the total size of your radiators (EDR), so the new boiler can be sized right.--NBC
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
    And two other thoughts -- if the leak is above the water line, there is no stop leak product that is going to work at all...

    And I've yet to see a leak which got smaller with time.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • MrVince
    MrVince Member Posts: 8
    Nicholas and Jamie, thanks for the heads up.

    The leak is luckily below the water line. It might be from a bad gasket but I can't be sure until the sections are taken apart.

    Have you, guys tried out a few of these products and if so, any that you particularly recommend that works better than the others? Any preference on liquid or powder?

    And, how long do these sealers typically last for you, guys? It's particularly cold where I am and to get my guy to even come out and price out the replacement was an ordeal. So, I'm hoping that the sealer will last for at least 2 months so I can do the replacement the right way. I don't want guys to do a half **** job.

    Thanks for the advice. And, Happy Thanksgiving!
  • nicholas bonham-carter
    Is it a seep, or dribble leak, as far as volume goes?
    I am sure they are all the same sort of chemistry, so prepare the occupants for some smells, (we used the gunk product, I believe).--NBC
  • Marz
    Marz Member Posts: 90
    We have the best luck with the Hercules Liquid Boiler sealer. Important that you follow the directions. By far the best product.
    kcoppGrallertdelta T
  • sullyno2007
    sullyno2007 Member, Email Confirmation Posts: 3
    Hair pine crack in under water level in gas water heater Burnham all origin
  • sullyno2007
    sullyno2007 Member, Email Confirmation Posts: 3
    Sorry what’s best product to deal pipe can stop leak use heat. Any help I can get. Was thinking muffler weld
  • sullyno2007
    sullyno2007 Member, Email Confirmation Posts: 3
    Used Hercules posdibilly incorrectly wasn’t hot when used. Worked shortly
  • delta T
    delta T Member Posts: 884
    I'll second the hercules. Only one I've ever gotten to work, do read the the directions in full though.
  • Intplm.
    Intplm. Member Posts: 1,997
    Have used Hercules and the Gunk brands. Both have worked well. It can buy you a few months threw winter till the warm weather arrives again.
    Be sure to follow the directions carefully. If you don't, you can fill the hole that is leaking but also fill a port in the boiler that needs to read water level or pressure etc.
    The Hercules is a bit more forgiving if you use a little more than required. I have used both for residential and commercial temporary boiler repairs.
    Do not trust these products to be a permanent fix. Treat it like a temporary fix until the leak can be corrected properly.