Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Air in heating system

emc4emc4 Posts: 3Member
Need some help here - I just bought my house a year ago, and am having a bad problem with getting air in my baseboard heating system. The entire system was bled in November, and by December the system was full of air again. It bubbles and makes tons of noise, sounds like there is a babbling brook running through my bedroom. We had it looked at and they said it was probably the automatic bleeder valve that wasn't working, so they bled the system again and replaced the automatic bleeder valve. Less than a week later we started having air in the system again, and it has gotten worse and worse. Our service company came back and basically said that they don't know whats wrong. Not sure what to do because the noise is so loud at the point it keeps me awake at night. I don't feel like the system should have to be bled every month in order for it to not be incredibly noisy, something is wrong. If the service company cant figure it out, what do I do? Its a 3 zone system, oil burner in the basement. The pressure relief valve drips, but they said that wouldn't have anything to do with the air problem... Please help!


  • JUGHNEJUGHNE Posts: 5,579Member
    Do you have old pumps? Sometimes pumps, which create a suction to pull water, can suck air thru the shaft seal while running. They don't leak water necessarily but allow air to be pulled in.

    This would only be pumps with exposed shafts.
  • Jamie HallJamie Hall Posts: 10,286Member
    Do you have a pressure gauge on the system? (you should!). If so, what does it read with the system cold, and what does it read with the system hot? And somewhere there is an expansion tank. You might take a picture of that and post it, or if there are labels on it just tell us what they say.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • emc4emc4 Posts: 3Member
    edited March 2017
    I have no idea how old any of it is because we only moved in a year ago. And the tech recharged the expansion tank when he was there in February. I will see what the pressure is when I'm home later.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,632Member
    Again all you need is a technician that knows something. Sounds like an expansion tank issue to me. The relief valve leaking also could point to and expansion tank issue. need pictures to help diagnose
  • GrallertGrallert Posts: 308Member
    For every drop of water that comes out of your relief valve, another drop is added through the feed. That new water is o2 rich. That's one way air gets in. Why is water getting out? My guess is that expansion tank has failed to hold its air charge allowing the water to expand through the relief valve. The relief could now be faulty as well as the feed (PRV). While your boiler is hot the temp. pressure gauge should be at or around 12psi if the gauge is good. If it reads near, at, or above 30psi start with a new expansion tank. Maybe a different service tech as well.
  • newagedawnnewagedawn Posts: 549Member
    yes i agree, sounds like the expansion tank but, could also be a faulty relief valve
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • RJ_4RJ_4 Posts: 484Member
    Make sure the automatic air vents are valved off after your done bleeding the system.
  • emc4emc4 Posts: 3Member
    edited March 2017
    When the boiler wasn't on (and hadn't been on for a while) the pressure was 15 PSI. Forgot to get a reading when it was on but in the past ive seen it above 20. The tech said his reading was the same as our gauge so the gauge works fine. I also found something dripping (see 4th picture), could this have something to do with the problem?

  • GrallertGrallert Posts: 308Member
    That drip is probably the packing nut on the valve stem. So there's another 02 rich drop being added. They add up. Over 20psi is pushing that tank very close to its capacity and any shock like a fast closing zone valve is going to test your relief. Especially if it's been weakened or rusty. Very often replacing any one of the pressure regulating components leads to the discovery of an issue with one or the other remaining components.
  • GrallertGrallert Posts: 308Member
    Looking closer I see it looks like the little drain cap on the supply water valve is whats leaking. tighten or replace the gasket.
  • clammyclammy Posts: 2,211Member
    i see u have 2 zones ,one them wouldn t happen to have piping thats entering your slab ?The air issues your having are they occuring on your upper floors ,if so i would to see if any of your heating pipes are entering your slab if that may be ur issue.Your service company should be smart enough to fiqure it out i would hope .A quick test would be to close your feed valve and see if the pressure drops if then you have a leak some where and unless theres a visable leak some where i would think to isolate and pressrize that slab loop and then figure out how to re pipe your slab supply zone.peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,632Member
    20 psi with the system hot is completely normal. The pressure will probably fluctuate between 15-20. If it does this as the system runs (higher pressure when hot, lower pressure when warm then the expansion tank is working fine. I agree, it's probably the packing nut on the valve leaking. Gently tighten it up
  • ZmanZman Posts: 4,817Member
    This system has the classic circulator pumping towards the expansion tank problem. Once the air get in, it is very difficult to get it out. It is likely not the cause of the problem but it makes it much more difficult to remove air once it is in
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • newagedawnnewagedawn Posts: 549Member
    looks like you have a bunch of issues there, i need to ask do you have a 3 zone, i see 3 honeywell zone valves there if so, that means you have 3 t stats,correct? if so YOU CANNOT RUN 3 -3/4 heat loops off a 3/4 main and return you need minimum 11/4" header on supply and return and then take the 3- 3/4 loops off that ,3/4 header only carries 39,000 btu a 1'' can only carry 71,000, a1 1/4 carries 160,000 and if you have 3 zones you will need a minimum 1 1/4 pipe to carry all the load, also you need an air scoop with an air valve on top and the expansion tank on the bottom in the supply,... the circulator can stay on the return, even tho its not in a the perfect spot, until you fix the pipe size, expansion tank and that air vent( an air vent is not an air scoop,lol) you will always get water leaking the heated water is to much for the relief valve to handle especially if the expansion tank diagram is busted, heres how you test that,... the top half is water ping it with your finger if its solid thats good now ping the bottom area of the tank if it doesnt sound hollow it has failed and water will continue to leak out the relief valve, if you like i can draw a diagram of how to fix your problem
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!