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What causes good automatic float type air vents to leak?

chapchap70chapchap70 Member Posts: 139
Two Taco automatic air vents on boiler.  One leaks.  I tried cleaning it out and reinstalled but it still leaked.  For the heck of it, I tried switching the autovents.  The one that was leaking did not leak at the new location but the other (non leaking one) leaked in the leaking location.  Switched back and the leak is because of the location; not the vents.

The only thing I can think of is there is more turbulence at the leaking location.  I am thinking the fix would be to add a nipple to make it higher. 

Did anyone else ever have this problem?


  • pipekingpipeking Member Posts: 252
    edited February 2013

    are they located on the system? got pics? are they on valves?
  • chapchap70chapchap70 Member Posts: 139
    Above the boiler

    The leaking location is in a 4 way black fitting above the boiler.  I'm looking more for a theory of why it would happen on any system.    
  • hot_rodhot_rod Member Posts: 13,184

    in the system? Temperature of the system at limit? Fluid quality? Any other air removal devices in the system. Fill water being added? Expansion tank working?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • chapchap70chapchap70 Member Posts: 139
    They are 2 feet from each other

    There is one maid o mist air vent at the high point of the system in one of the zones that has no problems.  The other two are above the boiler. 

    The system pressure changes about 3 to 4 psi cold to hot.  I have set it as low as 8 and as high as 20.  The pressure relief valve has never blown due to high pressure.  The flow is good.

    What is strange to me is why would one location leak water but not the other two feet away?
  • icesailoricesailor Member Posts: 7,265
    Float Vent Leaks:

    They almost ALL leak. I close the caps on all caps once purged and vented. I've never had a call back. I see white crud around all vents around the caps where they leak. Keep the system pressure over 12#, especially if the boiler is below the first floor and there is radiation on or above the second floor.

    If closing the cap stops the leak, and there is no adverse effect on the flow, why worry about which one leaks, where and why, just try closing it.

    If you are standing on top of a 6' step ladder, where you aren't supposed to stand, and you loose your balance, you will fall to the ground. You don't need to know why you fell (gravity), you just will. Not standing on the top of the ladder will stop the problem.

    I've found and changed hundreds of vents. They aren't cheap. I never had anyone question my changing them. But one day, I started closing the caps on ones that I had recently changed. I never had a problem or call back. Someone makes a lot of money by having us change them. I've seen more problems with vents sucking air from systems with undersized Extrol tanks or incorrect system pressures than I ever say by a lack of them.

  • heatpro02920heatpro02920 Member Posts: 991
    a thorn in your side...

    High vents have always been trouble in hot water systems, but people like to see them and they have been installed in a lot of systems... The good news is when they leak its hardly ever a reason for a service call, normally we deal with them on a tuneup or service call for a larger issue...

    I use the watts Duo vents for new installs and the taco 400s for replacements. When I install a duo vent I use the next size up tee so if it is in a 3/4" line I will install a 1" copper x 1/8 female x 1" copper tee with 2- 1 copper fitting adapter x 3/4 copper reducers, this allows the vent to work while the circulator is running, and works very well.. But after the cost of the vent and the fittings, there has to be a reason for me to install them, you can almost put a 3/4 sweat spiro vent for the same price... Needless to say on new systems I hardly ever install more than 1 high vent and that is normally on the unit itself per the manufacturers instructions... And on retro fits, I replace the existing vents with a new vent since its not a matter of if it is going to leak but when....

    Also a quick note, not a lot of people know with the duo vents, you leave the black cap loose and the red cap tight, with the taco I leave the cap loose..

    I have heard of old timers squirting a little oil lube in the bottom of the high vent and shaking them before installing them, I had a few techs work for me that were taught this and always did it, but I can't say if this helped or not, didn't seem to hurt, but I haven't seen anything to tell me it is worth the effort, I guess I never really paid attention to the results...

    Now as for your problem with a vent leaking in 1 place and not another, is this just when the circ is running or as soon as you put pressure to it?

    If a brand new vent leaks in that spot, I would just plug that hole.. No vent in that spot..

    If it is only while the water is circulating, I would just plug that hole with an 1/8" plug and be done with it.

    If it leaks as soon as you put psi to it, than, yes you guessed it PLUG THE HOLE....
  • hot_rodhot_rod Member Posts: 13,184
    vent tips

    you can add a hydroscopic cap to some brands of vents. This cap gives you a second shut off should you get a leak through the stem.

    Really the cap needs to be loose for an automatic vent to do its job. You can buy a manual key type vent if you just intend to use it at fill and start up.

    You can add a service check to allow you to remove the vent for service.

    You can add a threaded cap and put a tube to the floor so a leak doesn't damage anything below it.

    You can but an anti vacumn cap the prevents air from being sucked into a mis applied vent.

    They all work better with 5 psi or more to help get a tight shut off and at high points you really need to have some positive pressure to assure the system is filled.

    More often then not dirt or teflon tape shards are what cause a vent to leak, it's a fairly simple seal not unlike a toilet ball cock or a schrader valve on your tire stems.

    Many brands have a removable cap that allows you to clean them out. If you have a chronic problem it may be tie to put a hydronic cleaner in the system and power flush out the dirt and debris. maybe the system was never cleaned properly from day one?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • icesailoricesailor Member Posts: 7,265
    More vent tips:

    99.9% of float vent leaks I see, IMO are caused by water evaporation on the seat and finally fouling the seat. I find it more practical to just crank the cap down rather than take the time to go to the truck and look for a 1/8" brass plug. The cap is already in place. If a problem shows up after I leave, I will come back and deal with it. I've never had to go back that I can remember.
  • RJ_4RJ_4 Member Posts: 484
    air vents

    Automatic air vents should be isolated after original fill of closed hydronic systems. If you still have air in your system after that point you have a system leak which is causing the fill valve to add water and entrained air. alot of times a leak can be traced back to the relief valve opening.  This is is most commonly due to a water logged x-pansion tank.  I do leave automatic air vents active in open loop systems like cooling towers.  Like Ice Sailor said just close caps, next tme install a shutoff valve before the vent.
  • icesailoricesailor Member Posts: 7,265
    Vent Shut-off's:

    With the Taco 400's and Califfi solid brass flost vents, I consider them as being an air shut-off. A cheap valve and I don't stock 1/8" shut off valves. And all the 1/8" pet cock shutoffs, to be leaking and inoperable after a period of time. 

    Turn the cap on a Taco #400 and it doesn't leak.
  • Ron Jr._3Ron Jr._3 Member Posts: 594
    4 way black fitting

    An EK ? 
  • Ron Jr._3Ron Jr._3 Member Posts: 594
    edited February 2013
    Why have an auto air vent

    if you're just going to close it after fill up ? Would you cap a Spirovent or other type of fancy air eliminator ?  You can purge a boiler with high pressure for a good long time and still have air in the system when it heats up . I know it first hand and it happens quite often .

    Like Hot Rod said , a float type vent usually leaks due to crud buildup from the system . We don't usually add a cleaner to a new install . But we do purge hot , and don't open the float air vent till after the purge . Cause you know where all the system's crap is gonna wind up if you fill the boiler the first time and vent it at air vent on top of the boiler ................
  • hot_rodhot_rod Member Posts: 13,184
    materials of construction

    Caleffi uses a Viton seat and a stainless pin, perhaps less expensive brands use EPDM or BUNA? Maybe a plated brass pin that deteroiates? But really it should seal off air as well as water. Tire stems seal air for most of us on our vehicles, even without the plastic caps :)

    I'd guess many vents stick in the shut position after years of non use, just like fill valves, pressure relief valves, and T&P valves stick shut.

    The same mechanism used in most of the smaller Caleffi float style vents are used in large air and combination separators and those really need to remain open and un-capped to do the job they were intended to do.

    You'll start to see more and more multi-purpose devices that can handle air, dirt and hydraulic separation. So this one device is handling the air elimination for the boiler side piping as well as the distribution side. It may have a row of boilers connected to the device.

    Properly piped and with adequate flow you really should not need a bunch of remote float vents in the system, maybe a few high point or remote manifolds locations.

    The dirt separation function, in the multi-purpose devices, may be responsible for keeping those dirt and teflon particles out of the vent seat.

    As long as the air bubble can be pumped through the system, a good central air elimination or multi purpose air/ dirt device is all that is needed.

    We make separators up to 12" pipe size, costing several thousands of dollars. Their main purpose is to vent air, so I still am of the opinion that the caps need to be loosened.

    It's quite possibly a hydronic system that has been cold all summer will want to belch some air on first warm up in the heating system, or you may get the call for noisy heat emitters.

    It's a lot like the fill valve question, leave it open, or shut it off?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • icesailoricesailor Member Posts: 7,265
    Old System Venting:

    I just don't understand all the old systems I work on with no modern air separator devices that have been working for all these years have managed.

    Its a good thing that they don't pipe them like that anymore.

    Didn't Taco have a deal with Califfi and they made some of the equipment that Taco sold? Like the #400 float vents? My supply house had an Eat & Greet with a Califfi Rep. I couldn't tell the difference and they come apart and look the same.

    If you drain and winterize a heating system with a Spirovent, you have to cap off the vent if you want to build pressure. I forgot to remove the cap. It didn't make any difference. I leave them capped. If I was having air issues, I would remove the cap. When I do, I will remove it, So far, I haven't removed any caps.
  • Jean-David BeyerJean-David Beyer Member Posts: 2,662
    Properly piped and with adequate flow you really should not need a bunch of remote float vents in the system, maybe a few high point or remote manifolds locations.

    I was surprised when I had two 3-foot sections of baseboard replaced by two 14-foot sections upstairs in my house because the contractor did not put any air bleed valves up there. The former owner of the house had told me to bleed the baseboards every year, and that seemed to make sense, but I noticed I never got any air up there. Those air bleed valves were actuated by a little key. Anyhow, the contractor said you did not need them with baseboard. And that is sort-of true. The contractor did have purge valves and ball valves strategically located, so they purged the whole system from the ground floor garage.

    Now if there were any air in the system, it would pretty obviously collect in the upstairs baseboards, since they are the highest point in the system. And whenever the system needs a little draining (replaced a circulator, for example), they purge it and some more air gets into the system. But that has happened about twice.

    I do have a fancy Taco 4900 Series microbubble resorber down near the boiler that should get all the air out, and it does. Eventually. If there were so much air in there that the circulator could not pump the water around, it would be a pain, but as long as the circulator works, those bubbles dissolve in the water and come out in the microbubble resorber. It takes a couple of months to get it all out because the thing is in the secondary loop of the system (the loop where the boiler isn''t) and its temperature never goes above 135F. It would have been better if it were in the boiler loop, were the water goes up to 175F (to run the indirect): air could come out faster, but the contractor carefully followed W-M's installation manual as far as near-boiler piping was concerned.

    So as long as the air in there is small enough to permit the circulator to work, the air eventually comes out. I started heating, casually at first, around the beginning of September, and the air has been gone for at least a month now. John Siegenthaler thinks a week or two should be enough, but that is assuming it is in the system very near the output of the boiler, and mine is not.

    See page 2 and 4 of this.

    "Caleffi uses a Viton seat and a stainless pin, perhaps less expensive

    brands use EPDM or BUNA? Maybe a plated brass pin that deteroiates?

    But really it should seal off air as well as water. Tire stems seal air

    for most of us on our vehicles, even without the plastic caps :)"

    The Taco unit uses

    Housing: Brass

    PALL Rings: Stainless Steel

    Venting Unit Components: Stainless Steel,

    EPDM, Viton, Brass, and Engineered Plastics
  • hot_rodhot_rod Member Posts: 13,184
    didn't use to matter

    so much on then older boilers. Many had air elimination built in that did fine even without a scoop type vent anywhere.

    We evolved, realized a scoop with a float vent could add some benefit and that was the mainstay for years, worked fine. It still works OK.

    Probably SpiroTherm gets the credit for bringing micro bubble resorbers to the market. Realizing that more modern copper tube and mod con heat exchangers really wanted...needed the micro and entrained air out of the system to prevent hot spots and increase heat transfer.

    So air removel has improved, doesn't mean you NEED to use micro bubble removers, or any vents at all. But why not offer your customer the better technology. Air scoops and float air vents will not remove entrained air or micro bubbles. These "small" air cling to hot HX surfaces and reduce heat transfer. They eventually grow to larger bubbles and cause noise, possibly lack of flow.

    After all we don't go to work in a horse and buggy anymore.

    Unless you are Amish, even they are evolving :) They tie their buggies up to the local McDonalds near me every morning. They even have a special hitching post in the parking lot.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • hot_rodhot_rod Member Posts: 13,184
    the new movement is

    to design hydronics to operate at much lower temperatures. With mod con boilers we can gain efficiency by operation at lower temperatures. One goal is to design systems for 120F temperatures. Robert Bean threw down 100F as a goal at the recent RHC roundtable.

    Lower is good for GEO powered hydronic systems as well as solar thermal input.

    With radiant and generously sized panel radiators or forced convectors like Jaga or the new Runtals these numbers are doable.

    Lowering the fluid temperature makes it harder to remove air.

    This graph from I-dronics #12 shows that relationship. This is why it is so much tougher to rid air from chilled water systems. You really want a high performance air eliminator on chiller systems.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • icesailoricesailor Member Posts: 7,265
    Cool water pumping:

    What you say about cool and cold water pumping is true. However, you all are pushing systems that are not cold water pumped, but not differentiating the difference.

    You are convincing (through training) that a system will not run properly unless done like these super expensive, over priced and over designed systems. That rounds off to overly expensive systems. A simple system that becomes so expensive that a Scorched Air system will be chosen. Where's the profit in that?

    I see far too many of these BMW systems go in and someone else usually has to service them because the installers had no idea about how they worked and what problems they would be prone to. Or, when they figure out what is wrong from previous experience, they walk away because they don't want to be responsible for paying for the changes needed. Or the house is sold. They new owner has no idea that they bought a system that doesn't work well, and is a service persons nightmare.

    These systems are getting so complicated and expensive that Scorched Air becomes the choice. And  we all know how high tech that is.

  • chapchap70chapchap70 Member Posts: 139

    EK-3  Piped that way from the factory which is why I hesitated to think it was the location.  I even put in a new float vent and that leaked too on the initial call for heat.  
  • chapchap70chapchap70 Member Posts: 139
    Thanks for the replies guys

    It is interesting that one of the valves in the links submitted by Jean David has a limit of 5 ft per second.  I didn't look to translate that to gpm but it is possible that this system moves water faster than that at the vent location.

    When filling the boiler after the last time I had the system opened, I put about 20 psi in it and closed the valve after the boiler feed.  I believe in leaving it closed especially if I have occasion to check it once in a while and there is a lwco.  I only had to manually let air out of the now manual vent a couple of times and the system pressure went down to about 8 psi after a couple of weeks and stayed.  The automatic feeder only pressurizes to about 8 psi anyway according to the gauge.  The highest point in the system is less than 10 feet above the boiler and there have been no flow issues so it was operating that way for months.
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