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Hot water heating -- pressure valve open all the time?

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Thomsa
Thomsa Member Posts: 7
in THE MAIN WALL
I live in a 4-story brownstone with hot water heating. There's a valve connecting the city water to the heating system with a pressure gauge set to 20psi. Should that valve be open all the time so the system maintains the right pressure? Or should it be closed and only opened to re-pressurize the system from time to time?

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  • delta T
    delta T Member Posts: 884
    edited October 2016
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    I would only ever turn it off IF there was a Low water cutoff device that has been verified to be in good working order connected to the system.

    In theory, if the boiler and system is completely sealed with absolutely no leaks, then the fill valve is never used and the valve could be off.

    If however there is even a small leak, over time the boiler will require water to be added to it and the auto fill valve will do on its own as long as the valve is open.

    If there is no LWCO then I would definitely leave it open.
  • Thomsa
    Thomsa Member Posts: 7
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    This is very helpful, many thanks!
    How can I check if there is a low water cutoff? Where would it be located or what would it look like?
  • delta T
    delta T Member Posts: 884
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    take a picture of the boiler and the piping near the boiler.

    Is there some reason you want to turn the water off?
  • Thomsa
    Thomsa Member Posts: 7
    edited October 2016
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    Well... I'm renting and the landlord sends a handyman who apparently closes the valve after bleeding the radiators and filling the system. I don't have much faith in the handyman since he also considers it necessary to hold a shop vac to a radiator's valve when filling...
    I just want to make sure that nothing catastrophic happens if I leave the auto fill valve open.
  • Jamie Hall
    Jamie Hall Member Posts: 23,289
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    There should be a pressure relief valve somewhere on the boiler -- it will probably have an open pipe going to near the floor. Or it should. The only bad thing that could happen if you leave the auto fill open is that it might leak -- they do, sometimes -- in which case it will raise the pressure in the boiler higher than it should be. At which point, the pressure relief valve will open and drip, and you can see that.

    There might also be a pressure gauge somewhere... they are supposed to be there, but sometimes they aren't. That can tell you right away that things are as they should be.

    But bottom line -- the worst that will happen is that the pressure relief valve will open.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • delta T
    delta T Member Posts: 884
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    though.....the worst that can happen if the valve is left off, if there is no LWCO, is the boiler dry firing. This would take a lot to do however, and unless there is a large enough leak somewhere for the whole system to drain down to below the level of the boiler, it is very unlikely. If this were the case, it is likely that someone would complain of not having heat long before the boiler dry fired.

    That being said, I haven't seen the system and cannot make that judgement. safer to leave the valve open IMHO, as Jaime said the worst that will happen in that case is the relief valve dripping on the floor.
  • Thomsa
    Thomsa Member Posts: 7
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    This now makes a lot more sense to me. Last winter the radiators on the top floors never got really warm. The handyman came once to fill more water, apparently closing the valve again before he left. That helped temporarily with the top floor radiators but eventually the problem came back -- not surprisingly.
    Thanks to both of you for the explanations of what's going on!

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