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Why won't the fan coils stay heating???

sig Member Posts: 13
I just took over the service on a monestary. There is a 5 mbh boiler that was installed in 1949 and 2 new 2.5 mbh boilers installed a few years ago. There as some renovations done several years ago where carrier fan coils were installed thru out the rooms. It is a 3 story building with the rooms grouped as a wing. I can purge the air from the crappy coin vents in the fan coils to get heat them but as I make my way down the hall units that were heating fibre m fine stop working...I can do it all day and get the same result. There are is no main air eliminator at the boiler, there are no mechanical plans so I don't know how things are piped but it looks like the ends of them returns are run to a tank in the attic which is piped to a slop sink in the basement where I can open a valve and get some air out. I'm not the first guy to try and fail... but I hate failing... Any thoughts??


  • ratio
    ratio Member Posts: 3,655
    Find out where the hot water is, and figure out why it wants to go there instead of the fan coils.

    It isn't going to be easy, or terribly fast. Post some pics of the piping around the boilers. Start tracing out the pipes and try and figure out the water flows.

    Don't give up!

    EBEBRATT-Ed Member Posts: 15,635
    Can't give you much help without knowing what you have. I know it is a problem for you but what I would suggest is make a complete drawing of the system , at least the parts you can see. We may be able to fill in the blanks.

    Don't know it you can invest that amount of time in the project.

    For starters, some pictures would help. Boiler size, pump size(s) pipe sizes, expansion tank Attic tank?? etc
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    What sort of expansion tank is there
    On the system?
    If a bladder type, then there should be some sort of air scoop, but if there is an air cushion tank then that is part of the air elimination system.
    Some old systems had an open tank in the attic, with an overflow piped back down to a drain, and maybe that is the pipe you see at the sink.—
  • sig
    sig Member Posts: 13
    Thanks everyone... There is a extol tank in the mechanical and the tank in the attic is a fairly new galvanized tank. The old brother who lived there for many years turned me on to the valve in the basement... and it works for some of the building, just not the bedrooms. I have to get the pressure up to 30 psi for it to work though, but I can't leave it there as the old boiler isn't rated for anything other than a 30 psi relief so the system pressure usually is kept around 25. There is one pump for 2 floors of bedrooms, 52 rooms total and the tags are gone but it doesn't look more than a B&G 2".
  • Jamie Hall
    Jamie Hall Member Posts: 23,458
    That old tank you see in the attic is, almost certainly, the expansion tank -- and air eliminator. It must be open vented, as well as having the overflow drain -- and it must be connected to the system; you should not be able to raise the static pressure above what is required to make it over flow. If you can raise the pressure above that (and it sounds as though you can -- it should over flow at somewhere in the vicinity of 15 to perhaps 20 psi) -- it may be valved off.

    It seems to me quite possible that the renovation piping may have been done in such a way as to make it difficult to purge the system of air.

    Do give us as much of a diagram as you can!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England