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Where to put Air Eliminator

I have a boiler system that was installed 20 years ago. It was originally installed with one circulator pumping into the boiler. After reading Dan Holohan's Pumping Away book several times, I decided to change some the piping so I could have separate control of several zones. The two story house has old cast iron radiators in all rooms except one that has baseboard slant-fin type radiators. It never did keep up with the rest of the house. I moved the circulator to the outlet of the boiler and added another circulator as a separate zone to the room with the baseboard heat. I also added a Taco 4-zone relay switch and another thermostat to control the one room. The whole system now works as I planned, except when just the one room calls for heat the boiler cycles between 160-180* with a lot of thumping in the boiler the entire time. I think there is air in the system that is I can't get out because there is no air eliminator or air scoop. There is a diaphram expansion tank next to the boiler, I did not change any of that piping. There was a small manual bleed valve on top of the boiler that i replaced with an automatic vent, but that did not make any difference in the noise. There are bleed valves on all of the radiators and on the baseboard piping and I have bled all of those. Any suggestions on what type of air eliminator I need to add and where in the system to put it? The ones I have looked at recommend putting it on the outlet of the boiler before the circulators, but there is no horizontal piping runs to install it.


  • Rich_49
    Rich_49 Member Posts: 2,766

    to the left of where you took the second picture and take another showing all the piping on the side of the boiler , take a few others also so we can see all the piping and how it is run .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Magilla62
    Magilla62 Member Posts: 4
    Pretty Cluttered Area

    but here are some more pics if they help.
  • bill_105
    bill_105 Member Posts: 429
    Man, you got a project

    First off, what's the deal with the fill-trol valve and the tank almost on the floor?
  • Magilla62
    Magilla62 Member Posts: 4

    the expansion tank IS on the floor. That's the way it was installed 20 years ago and up until now I didn't have any problems with air in the system. Not sure what you mean by a Fil-trol valve. There is an automatic vent valve on top of the boiler by the PRV. I replaced a manual vent valve with the automatic and it didn't seem to have any effect on the air problem.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    edited February 2014
    Casual observations...

    Any time you have parallel pumps, each pump must have its own check valve.

    The top of the boiler makes a perfect air separator. Water at that point is moving at the slowest possible velocity, is in its hottest form, and exposed to the lowest mechanically induced pressure.

    One thing that really jumps out at me from your photos are the high amounts of rust on the niron components of the system. This is an indication of flue gas spillage occurring for extended periods of time. Make certain that the draft hood is not spilling products of combustion, and make sure you have a good CO detector on each floor and near sleeping areas.

    Also, that expansion tank MUST be mounted high enough to allow access to the Schroeder valve on the bottom of the tank. Otherwise you can't check or adjust diaphragm pressures. While you are at it, change the drop elbow on the tank to a tee, and put a drain valve in the open hole of the tee. This will allow you to creectly check the diaphragms pressure without having pressure on the other side of the diaphragm .

    Lastly, what you are describing isn't an air problem. That is steam flash occurring within the boiler. It could be the result of excessive fresh water induction, and subsequent liming of the heat exchanger, and associated boiling. I know it's called a boiler, but it is not supposed to be making that noise. Observe the pressure gauge when it it's thumping, and if the gauge is jumping in unison with the thumping, you have a need for chemical treatment to clean up the exchanger, which MAY result in the boiler leaking...

    Which zone is calling when you get the thumping? I am guessing that it is the BB zone...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • delta T
    delta T Member Posts: 884
    Air is not the problem

    Mark is right on. As Dan says: "if you bleed the radiators and get nothing but water, you don't have an air problem". I am sure by what you describe that you are hearing water flashing to steam in the boiler. I wonder if you have enough flow in the BB zone (or rather enough flow through the boiler when the BB zone is running by itself)? First thing is first though get those check valves in to make sure that you are circulating through the boiler and not just pulling back through the other zone with the BB pump. You said that you only hear the sound when just the BB zone is running correct? if that is so I am led to believe that you have do not have adequate flow through boiler when only that zone is running causing the boiler to heat up too quickly and thus you get the steam formation.

    As far as the air separator goes you already have one. As Mark said the top of the boiler will work very well as an air separator, in fact that boiler may actually have a little baffle in it to make the air separation even more effective (see p.57 in Pumping Away) so I would not worry too much about trying to put an external one in. However if you feel the need there are vertical air separators on the market. I know caleffi makes one and I'm sure there are others.

    Some more questions: Where is your water fill valve, and where does the fresh water tie in to the system? couldn't find that in the pics (unless I missed it) and what is your system pressure at? Oh and where does the return for the BB zone tie in?
  • Magilla62
    Magilla62 Member Posts: 4
    More Details...

    The water fill valve is on the return line above the boiler. In the picture on the right in the first post it is just out of view to the top right. I keep the boiler pressure around 18 psi, if I get below 10 psi the banging increases substantially. The circulator pump for the 1st and 2nd floors has a built in check valve (the green pump). The circ pump for the BB is the red one and it does not have a built in check valve. I think I have adequate flow to the BB zone because when the boiler kicks off due to overtemp (180*), the circulator keeps running and it only takes a few minutes for the temp to drop from 180 to 160 at which time the boiler kicks back on again. There is a 1 1/4" return line for all of the radiators that the BB ties into.
  • delta T
    delta T Member Posts: 884
    Does your pressure change?

    "I keep the boiler pressure around 18 psi, if I get below 10 psi the banging increases substantially"

    does your boiler pressure fluctuate regularly? do you have to add water? if that is the case then you need to figure out where the water is leaking from. Constantly adding fresh water as Mark said is bad for your system and will cause lime buildup as well as excessive corrosion of any ferrous system components (in your case most of them!) How long are the cycles when just the baseboard is running?