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Thread: New Gas boiler start up

  1. #1
    DIY Junior Member mat's Avatar
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    Default New Gas boiler start up

    Hi all, first time here, and I'm hoping someone can shed some light on what i think is a problem. I'm heating my shop with a natural gas boiler, conventional type, via 3 loops of pex in the concrete in a single zone. Last weekend i fired the boiler for the first time to begin heating the shop. Everything went fine, no issues with producing heat. After about 36 hours of operation and the heating call being satisfied and maintained, i happened to notice that the color of my supply and return pex tubing to and from the floor had darkened. Out of concern, i powered off the boiler and shut off the gas and allowed the system to cool so I could take a look at the water/glycol. Once it had cooled, i attached a hose to the boiler and drained about 2 gallons into a clean white plastic bucket. The glycol was as black as tar!!! I've been reading myself death trying to figure this out. I'm being lead to believe its corrosion/iron oxide from the cast boiler.... This fast? After letting the bucket of glycol rest a few days, the liquid cleared and the bottom of the bucket was covered with a layer (approx 1/8" thick) of thick black substance. So for fun, i took a magnet to the outside of the bucket and sure as I guessed, the sludge pulls to the side of the bucket, so its definitely containing iron. My boiler is cast, floor tube is oxygen barrier pex, pump is cast, and connections are 3/4" copper.

    Guys help me out here, is this normal? I feel at this rate i'll have no boiler left by the end of the season?

    The glycol mixture was approximately 40%.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Can't say for sure, but the water you filled the system with will always have some disolved oxygen gas in it. After awhile, that reacts with whatever it can and the system goes into equilibrium. So, once all of that gets reacted, it should be stable. If it leaked and you had to add water, or you got air injected into the system from say a pump seal, then it would continue. That's the reason for the oxygen barrier, so no new air can get into the system. See what the pros have to say.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Network Engineer rmelo99's Avatar
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    Well my house is o2 barrier pex some red some opaque white. The loops do get dark when running via my cast iron boiler. unless you have a leak somewhere then I wouldn't be worried. Draining water only to have to add more fresh in is doing your more harm. I understand you were just worried but it sounds like your have all setup right. I would suggest that you recheck the pex and make sure it was oxygen barrier(someone could have screwed up)

    then you could be killing your boiler. I have pex/copper/iron pipe/cast iron pumps and my water is never BLACK, but it certainly isn't clear. Before I rezoned my system and first drained my boiler and all the black pipe, the stuff that came out was like oil/tar. Not knowing how long before it had last been filled or drained I just assumed that's what decades of boiler water looked like.

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    DIY Junior Member mat's Avatar
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    Thanks remlo99. I am glad I'm not the only one who has seen something like this. I will check my pex.... its now in 6" concrete it better be O2 barrier as I specified!

    So I've had the system shutdown since discovering this issue as I want to make sure if i missed something that prevents (what looks like accelerated wear) this i can fix it now before I do any further harm. Since the black stuff has made its way through the system, i am wondering what I should do to flush it out before I refill the system. I don't think leaving it there will do any good. Is there any flush additive or something that will aid in removing this and/or prevent or slow it form happening again? I've found some additives online, but I'm unsure if its necessary or not.

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    Network Engineer rmelo99's Avatar
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    There are flushes out there to clean boilers and rust inhibitor additives. You mentioned you don't run straight water. How do you plan on refilling the glycol in there? If I remember correctly it isn't cheap to just purge all that glycol and have to refill with new.

    I would say run it with the black in there, but not having seen it you would be a better judge of how "bad" you think it is.

    BTW: if it does turn out to be a screw up on the pex, there are ways to isolate the ferous parts of a hydronic system without a tearout, it involves an exchanger and new non-ferrous pump and some repiping. Just in case you were concerened about that. It certainly is cheaper than redoing it all if it comes to that.

  6. #6
    DIY Junior Member mat's Avatar
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    Well i think for now my best approach is going to be to clean it out the best I can and see what happens. What i was thinking, to purge the system, i'll use my transfer pump and a few buckets of clean water and push that through until it flows clean. The glycol isn't cheap, (~$100 / 5gal pail) but with our climate I wouldn't go without. We've already had a week of -30C weather.

    I checked my pex, it's O2 barrier as I had thought.

    Do you know of any brands of flush chemicals or additives? Any you've had experience with?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You can fit it with a filter, but be prepared to check and clean or replace it until things are cleaned up some. It probably isn't necessary, though.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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