Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Boilers - Glycol & Anti-Leak Chemical


Our heating guy recently placed gylcol and anti-leaking chemical into our boiler heating system. However, we have weird issues with tons and tons of air in the pipes, having to bleed it like crazy. As a result, all the glycol and anti-leaking chemicals have already leaked out.

Our heating guy says the reason is because we had shut the boilers down in the summer, they had filled with lots of air, which had to be bled. But, our maintenance guy, when bleeding the pipes, realized that there was a significant amount of bubbles and lumpy gas leaking out, looking like it clogged the pipes.

So, basically, I am wondering if glycol and the anti-leaking chemical do not mix well with our system OR if is really just because air filled up while the boilers were down.

I would like to use the glychol and anti-leaking chemicals if possible, for obvious reasons.

If anyone has experience, please advise. Thank you!


  • pecmsg
    pecmsg Member Posts: 4,684
    Anti leak chemicals I wouldn’t recommend them. Find and fix the leaks.
    Glycol if there’s a chance it can freeze but I also try and avoid it.
  • Jamie Hall
    Jamie Hall Member Posts: 22,897
    I'm with @pecmsg on the anti-leak chemicals -- bad news. Ditto glycol.

    On the air. Just shutting the boiler down should not have allowed air into the system, unless it was also drained (which it needn't have been). However, if it wasn't run all summer the anti-leak chemicals may have "clotted" (one reason -- of several -- I won't use them), particularly in the narrower passages of the boiler, and it may take considerable flushing and then purging -- not just bleeding to get rid of them. Depending on the type of air separator you have, or any filters, they may have clogged those, too, adding to the fun.

    If your system doesn't require glycol, thoroughly purge it -- all pipes and radiation and the boiler -- then fill it with water to the required pressure and set about bleeding.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 21,835
    What type of leaks are you trying to seal? Sealers can work for tiny seeps or pin holes. They need to be approved for the glycol you have and carefully blended.

    Air not removed will go into solution when systems cool, then come out as the system heats for the first time.

    Need to have a quality micro bubble type separator mounted at the boiler supply outlet

    Circulator needs to pump away from the expansion.

    Fill pressure needs to assure 5 psi at the highest point. Height from boiler to highest radiator x .05 assures adaquate staticpressure.

    Manual or float vents at any high point.

    A good power purge when you fill or add chemicals.

    It’s a multi step process to rid systems of air, once circulating the air purger will take all the large and micro bubbles.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream