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Air Problems

Hoping you all can offer some help. I have a two floor apartment on the second and third floor of a building. (First floor has its own boiler). Last winter I had a freeze up of heating pipe in an unheated crawl space in the attic...I repaired it. Put heat tape on it and insulated it. I also since the system was empty and hadn't been serviced by the previous owner cleaned the boiler, replaced the expansion tank, auto fill and relief valve. Since that repair I have constant problems with huge amounts of air. I'm bleeding it weekly. I've forced purged it by opening the auto fill and using the bleeders in the basement as well as bleeders in the baseboards. The system pressure is 18 psi and I've replaced the temp pressure gauge on the boiler as well as used a temp one to verify the pressure.
While investigating this issue, in the eaves upstairs I found a pipe that connects two bedrooms. This pipe is the highest point in the system. To allow for access to the eaves they brought it up about 4 feet, it runs about 30' from the front to the back of the house and back down 5' to the baseboard in the back room. At each end of it on the high point there is a 90 elbow with a hy-vent in it. I thought perhaps these were the issue so I replaced them. And yeah when I took them out I let quite a bit of air out. I let the system heat up and run for a bit and bled the baseboards (not much air) and loosened the two vents I installed and again got tons of air out there.
Two nights later I could hear it gurgling again. I bled it again both at the radiators and when I got no air, did a purge in the basement again and got huge amounts of air out again. it ran fine, no noise. We just had a three day warm spell and the heat didn't run. Last night it got cold, heat came on and....gurgling again. I've inspected every inch of it for leaks and cant find any anywhere. I've even poked my inspection camera in the walls to look pulled the cover off the boiler and looked for a leaking heat exchanger. Its an older Burnham 160,000 btu boiler..... . So my questions....

1- I was told that automatic vents shouldn't be used in the attic because they are prone to leaks and when used in high spots like that they can suck more air into the system than they let out? Any input on this?

2- Am I missing something? I'm assuming if air is getting in water must be getting out somewhere?

Thanks so much for your time.


  • hot_rod
    hot_rod Member Posts: 16,293
    What type of air purger is back at the boiler. That central air purger does most of the work. The auto vents help catch air trapped at high points, they are not really the "air purger"

    Some times you need to do a power purge on problem systems a high pressure, or high flow flush. Bypassing the fill pressure may work, other times you need a purge cart that cn move 10- 15 gum to purge a large system.

    The pump should be pumping away from the expansion tank. a pic of the boiler piping may help.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 1,562
    edited December 2019
    There isn't any reason to have a float vent in the attic. I have removed them and installed a Caleffi hydrostatic coin vent instead or just a plain ole coin vent. Once the air is eliminated, I close them off.

    Pics of the boiler sys would be helpful. A Caleffi purge cart would be helpful for the professional, but not cost effective for a home owner. I use a lawn pump that has shut off valves that I put on it to purge my systems. You would be surprised how much crap and dirty water is expelled before the clean water and air bubbles come pouring out. All the air that's left in the water is entrained air which the micro bubbler removes.

    If you're not using Glycol, a cheap way to do it is to connect a garden hose to each circuit and the boiler drain and and use house pressure to push water thru each circuit. Close off the hose valve before closing the boiler drain or you will push open the pressure relief valve on the boiler. You might have to close the auto fill valve. Some auto fill valve have a fast fill option that you can use instead of a garden hose to each circuit.
  • Jamie Hall
    Jamie Hall Member Posts: 18,925
    Three floors plus the attic? 18 psi is only just barely enough. In fact, if you pumping towards the expansion tank, rather than away, it isn't enough, and even the slightest air leak in those automatic vents will suck in air.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Peterug13
    Peterug13 Member Posts: 7
    Little follow up on this. I did remove the two by vents and replaced them with the manual valve type. The problem persisted even thru replacement of the boiler. During a recent project I had occasion to cut open and wall and buried inside it at an elbow was ANOTHER HyVent. I removed it and replaced it with a manual valve and will install an access panel. I guess in the next few days I will know for sure! 
    EBEBRATT-Ed Member Posts: 11,995

    Old thread.

    The location of your pumps is important depending on the flow resistance of the system. I hope when the new boiler was installed they installed the pump(s) to pump away from the boiler.

    If not you could be sucking air in through a return if you have hi vents, even without hi vents the system will work better pumping away.

    You system pressure as @Jamie Hall mentioned is important. I would measure from the high point in the system to the top of the boiler.

    If you get 30' for example you need 2.31 feet/lb of pressure so30'/2,31=13' +4 psi so in this example you would need 17psi minimum
  • Peterug13
    Peterug13 Member Posts: 7
    They did install the pump in a pump away fashion. All the hy vents have been removed from the system piping. I realized it was an old thread….just updating….
    I appreciate all the assistance. Things seem to be much quieter and comfortable 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,192

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org