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Re-filling Hydronic System

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LmAcres
LmAcres Member Posts: 7
Hi Everyone
Time to refill my system after some major renovations. A coworker has said that I should close the domestic make up water valves once the system is filled and bled, but I thought they are to remain open? The (2) yellow valves are currently in the closed position in the picture, but this coworker has me questioning what I thought to be true. He's a retired homebuilder and knows his stuff, but hoping I could get a second opinion.
Thanks

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  • Zman
    Zman Member Posts: 7,573
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    You have just tapped into a long-term debate. If you close them, what is there to prevent the boiler from running dry and melting down? Personally, unless you have a low water cutoff (I don't see one in the picture), I think you should leave them on.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    TinmanSTEVEusaPALmAcresmattmia2
  • Tinman
    Tinman Member Posts: 2,808
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    “He knows his stuff”? That’s a recipe for disaster without a LWCO. 
    Steve Minnich
    LmAcres
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    Before refilling you can easily put a LWCO right there.

    There was an error rendering this rich post.

    LmAcres
  • LmAcres
    LmAcres Member Posts: 7
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    “He knows his stuff”? That’s a recipe for disaster without a LWCO. 
    He may assume that I have one, but I've also heard of people leaving the water open either way.
  • hot_rod
    hot_rod Member Posts: 22,262
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    For about 50 years now I have been installing and leaving fill valves open.

    I suppose one flood or lawsuit could have changed my mind :)

    Another option is to use a fill tank, like an Axiom. Or a homemade fill take built with an expansion tank and prv. You want to maintain pressure on a newly filled system as it will purge air for several days or more, until multiple heating cycles drive the entrained air out of solution. A purge alone will not accomplish that.

    I third the LWC, regardless.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Tinman
    Tinman Member Posts: 2,808
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    hot_rod said:
    For about 50 years now I have been installing and leaving fill valves open. I suppose one flood or lawsuit could have changed my mind :) Another option is to use a fill tank, like an Axiom. Or a homemade fill take built with an expansion tank and prv. You want to maintain pressure on a newly filled system as it will purge air for several days or more, until multiple heating cycles drive the entrained air out of solution. A purge alone will not accomplish that. I third the LWC, regardless.
    In my experience with a properly piped boiler and a good air separator, the time needed for system air removal can happen within hours. Before people started pumping away and were still using an air scoop, sometimes forever it seemed. 
    Steve Minnich