Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

kettling boiler and air in hot water boiler system

Hello, i am a service tech for several styles of equipment.
i am preparing to go look at a kettling hot water heating boiler , that has a definite history of having air in the system.
Owner has had to bleed air from a couple of areas in house several times a year for a while (only owned house 2 years).
I think at this point the noise from the kettling boiler is the main complaint.

My thoughts in the past were that if a boiler was making kettling noise, then the boiler was limed up.
BUT , i have a fellow service tech that had kettling on a new install , and his turned out to be not limed up (obviously due to age of boiler) but it was that there was no air removal device and he did a poor job of bleeding the system. Once he got the air out the system the kettling stopped and problem solved.

On my near future service call here , i believe that there may be a leak in the system , or that the fill valve is overfilling and then maybe the safety relief is blowing. Either way i believe the system is turning over a large amount of water. Hince to addition of air to system. And the boiler may be limed up or it could be just too much air in the system.

I am going to tear into the system check it out , test for leaks and investigate the air removal potential of the system, and try to decide what's going on.

I was starting this discussion to see if anyone had any advice or feedback on kettling, system air, and de-liming do's and dont's.

Thank you , All.


  • Jamie Hall
    Jamie Hall Member Posts: 20,416
    First thing I'd do is take a quick look and see if the thing is even piped correctly. Which is to say the auto feed valve connection and the expansion tank very close to each other, and the system pumping away from that connection -- again, without much space between the expansion tank connection and the intake to the pump.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    SuperTechdelta T
    JUGHNE Member Posts: 10,278
    There are some vents that will let air suck in.
    Depends upon the piping and if the air vent is on the suction side of the pump location.
    That has been on a couple of postings recently.
  • Steve_Wheels
    Steve_Wheels Member Posts: 24
    Turn the fill valve off after you purge to make sure you don't have a leak. A small drip on a packing nut, or a air vent behind the baseboard weeping are enough to introduce significant water to introduce air in the system. Is it a condensing boiler or an atmospheric boiler?
  • cashheatandactech1
    cashheatandactech1 Member Posts: 10
    i believe it is an "older" atmospheric. (Steve Wheels). But have not laid eyes on it yet.
    Thanks for comments, ALL.
  • Steve_Wheels
    Steve_Wheels Member Posts: 24
    cashheatandactech you can just call me wheels :-) What type of system did it end up being? find out anything?
  • Intplm.
    Intplm. Member Posts: 1,417
    Checking for a leak is a good idea as cold water feeding a boiler over time also adds air.
    I wouldn't be surprised if the system has a air scoop. An old style air eliminater with a hi-vent installed on top.
    If you do find that this is what is installed, that would be the first reason for these continued air problems.

    Piped correctly as @Jamie Hall stated is also a absolute must.

    @cashheatandactech1 when you get to the system, take some pictures at different vantage points and post them here . This will help for a better discussion.
  • SuperTech
    SuperTech Member Posts: 1,854
    Take some pictures and post them. The most important thing is that the circulator should be on the supply pipe and pumping away from the expansion tank and air separator, if it has one. If it doesn't meet this criteria recommend piping alterations. Install a microbubble resorber type air eliminator such a spirovent or Caleffi Discal. Install it on the supply pipe and connect the water feed valve and backflow preventer to it, as well as the expansion tank. Move the location of the circulator so it's Pumping Away from the expansion tank and I promise you that you will not have any air issues after purging the system.