Monoflow heating system/ Air in system

Discussion in 'HVAC Heating & Cooling' started by emattera, Feb 5, 2008.

  1. emattera

    emattera New Member

    Messages:
    8
    My house has monoflow hot water heat. Since buying the house we have made a couple changes, nothing major to heating system. The problem I have is that I cannot get the air out of the system. I have gotten it to a point that you could not hear any air flowing in the pipes but then a day or two later its back. My wife thinks I am nuts, spending countless hours bleeding and searching for air/water leaks to eliminate this problem.

    A friend of mine said that this is a common problem with this type of system, and if I wanted to keep it this way that I need to make a couple changes. These being to install an "air scoop" ( to remove the air in the main loop)and a new expansion tank (current one is the original bladderless type).

    Any insight and advise would be appreciated. Thanks, Ed
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,488
    Location:
    Cave Creek, Arizona
    air

    Air in the system has nothing to do with it being a MonoFlo system. And all systems need some type of air removal device, although many MF systems had a BoilerTrol which separated it at the boiler. A new expansion tank will also not do anything to cure it. The most likely source of ongoing air problems is a bad seal at the pump which allows air to enter but not water to leak out.
  3. emattera

    emattera New Member

    Messages:
    8
    I installed new gaskets on the circulator pump this year and it has not helped. Other than the bleeder valves on the baseboad units there is no other way to let air out. Given this, should I install a "bleeder valve" in the loop pipe? and if so what is the correct location?
    Thanks Ed
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,893
    Location:
    New England
    Did you install an air scoop? One brand is Spirovent...there are others. All closed systems need something. I'd replace the expansion tank with a bladder type. They last awhile, but put a shutoff valve to make changing it easier when the time comes the next time.
  5. emattera

    emattera New Member

    Messages:
    8
    On which side of the boiler would the air scoop and expansion tank be installed?
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,488
    Location:
    Cave Creek, Arizona
    boiler

    At the boiler's outlet to the radiation. Gaskets on the pump's flange have nothing to do with air entering the system. If they were the problem, water would be leaking OUT. The pump's shaft seal is in a low pressure area, which is why it can move water, but it is also where air can be sucked in if the seal is going bad.
  7. emattera

    emattera New Member

    Messages:
    8
    By seal I am assuming you are referring to the shaft seal. For what it costs I will just replace it at the same time as adding the air scoop. I guess that answered all my questions, now it is just a matter of putting it together and doing it.
    Thanks for your time. I will be back once I have the parts to make sure they are right and installed correctly.
  8. geno54

    geno54 New Member

    Messages:
    29
    What type of circulator do you have on the system? Model?
    Has the boiler been replaced in the past?
    What pressure is indicated at the gage?

    You could put in an air vent like a Taco 400 to automatically vent the air at the convectors, but you still want to resolve how air is getting into the system.
  9. emattera

    emattera New Member

    Messages:
    8
    The circulator is a Taco Model # 007-BF4-JW.
    The pressure gauge says 20-21 psi.
    Boiler is about 15-20 years old, based on what I was told when I bought the house. On the boiler sticker it says A-1989 in the bottom corner leading me to believe that was when it was built.
  10. geno54

    geno54 New Member

    Messages:
    29
    The pressure is hi enough so air is not being drawn in say at a hi point. The circ is a cartridge type and not open type with seals like a B & G 100. You could put in a Air scoop but that would only deal with the air in the loop. Once the air gets into the convectors the only way to get it out is by a manual or automatic vent. hence the Taco 400.
    Is it possible you have a leak somewhere and cold water keeps feeding in a little at a time? Are you literally getting air out of the vents or are they just not heating up?
  11. emattera

    emattera New Member

    Messages:
    8
    I have searched and have not found any leaks. Only one convector lets air out and the rest only let out water now. What is funny about this situation is that today it could sound like a waterfall and then in a couple days its just a couple air bubbles. But the problem is that it will do this in cycles ,bad then good then bad then good. I do need to bleed out the one convector on a regular basis so that it will still function properly.

    This problem has been on going for years now and has been very frustrating. It would be nice if it would just leak water, to say hear I am come and fix me.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,893
    Location:
    New England
    I didn't re-read the whole thread. Do you have an expansion tank in the heating system? If you don't, add one. If you do, are you sure it is both charged with the proper amount of air and is not shot? Not having room for expansion as the system heats and cools can create some big stresses on things and suck air or blow water depending on whether it is expanding or contracting.
  13. emattera

    emattera New Member

    Messages:
    8
    it is a bladderless expansion tank. You know the old style mounted up high in the floor joist and looks like a drum/barrel.
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,893
    Location:
    New England
    Are you sure it isn't waterlogged? One with a bladder would likely provide more reliable service. The inlet could be corroded shut, too.
  15. emattera

    emattera New Member

    Messages:
    8
    I am not sure what water logged means. But I have emptied the tank on several occasions with somewhere near 10 gallons of water coming out of the tank. The proper amount of water that is supposed to be in the tank, I don't know.
  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,893
    Location:
    New England
    There has to be an air cushion in the expansion tank, or it can't do its job. I'm not sure how they maintain an air cushion, as air is normally absorbed by the water since it is in contact, and hopefully, extracted as air is what allows corrosion in a system. A bladder type tank has no air contact (until it needs replacement) and will allow an air extraction device to work properly and maintain low air (and therefore oxygen which allows things to rust) in the water. I'm not a pro, but I'd replace that expansion tank with a bladder type.
  17. krow

    krow Plumber

    Messages:
    906
    Location:
    Ontario, Canada
    The only thing I would change on the monoflow system is, to install at least 2 automatic air vents at the highest points of your heating system or if that is not possible, you can install 2 ball valves with a hose bib in between.

    This will allow you to isolate each side of the valves and bleed the air from the hose bib with a high flow rate. Shut off one side and then bleed from the hose bib (attach a standard garden hose to hose bib). Re-open valve and shut off the other side and re-bleed. It may take a few tries to get it all out. You can have more control by throttling the valves.
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