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expansion tank gravity system

Timco Member Posts: 3,030
I have a cust with a gravity system working well, but it seems it has lost it's tank. Issue is, there is no pipe through the roof. My auto-fill runs up to 12 where it was set, and the pressure trips relief valve when hot. I have not seen a closed gravity system. Might the attic tank be a closed type?? Not a new roof or anything like that. I'd like to ID the problem with minimum attic time. Can a modern diaphram type tank be used with a gravity system? I cannot see a problem, but I may be missing something...

Just a guy running some pipes.


  • rjm
    rjm Member Posts: 60
    no expansion tank

    One of my co-workers was at a job a while ago with the same issue. I believe,originally that the radiators were partially full of air, and were used for expansion. New homeowner move in and bleed the radiators. No air, No expansion.
    But I don't see any problems with adding a diaphragm tank.
  • bob_46
    bob_46 Member Posts: 813
    Lost it's Tank?

    Tim, Where did the tank go? It might be prudent to find the tank and associated piping, disconnect it and cap it, then install a diaphragm tank. I wouldn't ****-U-ME that it won't cause you problems in the future. .02 bob
  • Timco
    Timco Member Posts: 3,030

    When I say "lost it's tank", I mean it is very sensitive to a small addition of water, and the pressure climbs very fast with the a call for heat. I have a plan to peek in the attic, but I have followed & accounted for all pipes in the basement, and none go to the attic. (small house) I did bleed the rads after I filled the system when I installed a new PRV / relief valve combo B&G unit.

    Just a guy running some pipes.
  • Dick Charland
    Dick Charland Member Posts: 178

    Check the attic, if this has a PRV on it, it has to be a closed system as you well know, my suspicion would be someone changed the open tank in attic to a "closed" tank when they changed it from a manual feed. They didn't necessarilly have to run the pipe from the basement, there may be an open pipe running from the tank to basement.
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