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How to *correctly* bleed system?

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hwb221227
hwb221227 Member Posts: 14
I've tried to bleed my system several times but still hear air gurgling through the boiler (not in the zones). I've started with the indirect tank on the bottom and then worked my way up to the two first floor zones and finally the two second floor zones. It sounds like there is air trapped in the boiler and/or the indirect loop. How do I correctly bleed the entire system?


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  • hot_rod
    hot_rod Member Posts: 22,327
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    I don't see an air separator anywhere on the system, just a couple air vents.

    So a purge will get some big air bubbles out, but adding an air removal device would clean it up without needing to purge. But it would involve a major repipe to do it correctly.

    Moving the expansion tank upstream of the two pumps would help also.

    With power off, a manual purge, put a hose on that drain valve above the black circulator, shutoff that yellow valve.
    Put the fill valve into fast fill position and purge from the hose.

    I would do one zone at a time by manually opening those zone valves

    The indirect purges by the green circ, yellow valve off, purge from hose valve to left of green circ.

    When the fill valve is put int fast fill position, pressure could rise above to 30 psi relief valve, causing it to discharge.

    A good job for a hydronics guy that is familiar with things that can go wrong with these steps might be a wise investment :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    hwb221227
  • hwb221227
    hwb221227 Member Posts: 14
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    hot_rod said:

    I don't see an air separator anywhere on the system, just a couple air vents.

    So a purge will get some big air bubbles out, but adding an air removal device would clean it up without needing to purge. But it would involve a major repipe to do it correctly.

    Moving the expansion tank upstream of the two pumps would help also.

    With power off, a manual purge, put a hose on that drain valve above the black circulator, shutoff that yellow valve.
    Put the fill valve into fast fill position and purge from the hose.

    I would do one zone at a time by manually opening those zone valves

    The indirect purges by the green circ, yellow valve off, purge from hose valve to left of green circ.

    When the fill valve is put int fast fill position, pressure could rise above to 30 psi relief valve, causing it to discharge.

    A good job for a hydronics guy that is familiar with things that can go wrong with these steps might be a wise investment :)

    There's a few Taco auto-bleeders one at the top most part of the return and one on the fresh water inlet. I'm wondering if air will just work itself out. I pretty much did that exact procedure you mentioned with ~20PSI by working the fast-fill valve. Not sure why I still have air after this.
  • leonz
    leonz Member Posts: 1,165
    edited December 2022
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    Every time I see a rat's nest of plumbing like this I shake my head.

    You can also turn the thermostat way up and let the heat push the bubbles out.
  • hot_rod
    hot_rod Member Posts: 22,327
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    As the water heats from fill temperature it displaces air, so a good purger grabs that air and gets it out.
    The vents you have are high point vents, designed to get any air that rises up to them. Nothing in the moving fluid stream to grab the small bubbles.

    The pumps to expansion tank detail is also working against you also. When you pump away from the expansion tank, them, pumps add their differential, that helps air stay in the fluid and get to the purger.. Them opposite happens with your system.

    What temperature are you running? Increasing temperature helps drive air out of the water.

    But without a purger it is going to be a long slow process to get all the air out.

    Every time you add any fill water you add air, and you are kind of starting over.

    The vent above the black circ could actually be pulling air into the system, depending on fill pressure and circ pressure differential, see them two examples inn the attachments. Try tightening the cap on the vent above the black pump after you purge, it may be working against you.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    hwb221227
  • neilc
    neilc Member Posts: 2,711
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    close that vent above the circ, and any other vents before the circ(s)
    leave the one on the supply open, and any others on the supply side open,
    looking again, are there any vents on that supply side?
    is there a vent on the boiler?
    picture of safety valve ?

    what pressure are you set to, and seeing on the tridicator?
    known to beat dead horses
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited December 2022
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    leonz said:

    Every time I see a rat's nest of plumbing like this I shake my head.

    I kind of think that is pretty easy to follow plumbing. Just because the manifold is not attached to within 3" of the wall, does not qualify for a Rat's nest In my opinion. Although My zone manifold is within 3" of the wall and is supported with split ring pipe hangers and all-threaded rod, I would complement the installer on this job.
    hot_rod said:

    I don't see an air separator anywhere on the system, just a couple air vents.

    Regarding the Air Separator there is an air separator built into the boiler. And... there is an air vent connected to it. I know this because of the very first Weil McLain Gas boiler I installed. I found out the hard way that there is a 1/2" or 3/4" tapping next to the 1-1/2" supply tapping. Here is that story: https://forum.heatinghelp.com/discussion/comment/1701242#Comment_1701242

    I believe that Air Separator is in the best location for the way it is piped. The only thing that could be better is if the Circulators were on the Supply Pipe, then they would be pumping away from the PONPC.
    leonz said:

    You can also turn the thermostat way up and let the heat push the bubbles out.

    I think this is the best advice. Along with the air vents on the return side being closed permanently, If the water pressure drops on the inlet side of the circulator pumps, (the returns) and the boiler pressure is low for some reason, those vents will let air in just as easily as they would let air out. The most important vent to leave open is the one at the top of the ¾” pipe where the expansion tank and feed valve is attached.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    hwb221227
  • hwb221227
    hwb221227 Member Posts: 14
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    The top end temperature is set to 180F and cold is configured for 15PSI. It does hit about 19PSI when completely hot. I ran the indirect by itself for a while and then each of the zones going up that ladder and when I got to the top return I heard some air purge. One thing to note is that when I installed smart thermostats (ecobee) a year ago I had to turn off priority on the Taco ZVC406 because it would kill power to the devices when the hot water tank would call. Could this be causing issues because the circulators can both run at the same time?
  • MikeL_2
    MikeL_2 Member Posts: 500
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    Hwb,
           Dan's book " Pumping Away " is a great read & bargain at about $ 25.00.......
    hwb221227
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited December 2022
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    hwb221227 said:

    The top end temperature is set to 180F and cold is configured for 15PSI. It does hit about 19PSI when completely hot. I ran the indirect by itself for a while and then each of the zones going up that ladder and when I got to the top return I heard some air purge. One thing to note is that when I installed smart thermostats (ecobee) a year ago I had to turn off priority on the Taco ZVC406 because it would kill power to the devices when the hot water tank would call. Could this be causing issues because the circulators can both run at the same time?

    Not likely
    The two circulators operating at the same time are not powerful enough to drop the return side pressure from 12 PSI to VACUUM. A vacuum below ambient air pressure is what would be required to draw air into the open air vents on the return.

    When was the last time you tested the air pressure in the expansion tank? That pressure needs to be tested when there is no pressure on the water side of the tank. There is a possibility that the membrane of the tank that separates the air and the water may have just started to leak air bubbles. If that has already happened then the tank must be replaced.

    I have read that air can pass thru the membrane at a rate of about 1 PSI per year. The air passes thru the membrane on a molecular level, like osmosis. So if the pressure in the tank has not been checked for 5 years and it started at 12 PSI, then you can expect to find the charge as low as 7 PSI and still have a good tank. Just pump it back up to 15 PSI (because 15 PSI is where you operate your boiler) and put the tank back into commission.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    hwb221227
  • hot_rod
    hot_rod Member Posts: 22,327
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    Maybe check to see if the float vent is actually working. The float can stick, needle valve plug, even the opening in the cap can plug.

    While there may be a low velocity chamber in the boiler section helping remove air, it is not as efficient as a micro bubble type air sep, especially on hard to purge piping arrangements.
    Which is why the Spirotherm was invented.

    Dropping below atmospheric can happen with a combination of low static and the resistance of the piping loop. Any other auto vents up higher in the system?

    Boosting the pressure to 22 psi for a few hot cycles can sometimes get the last air out of solution and gone.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    hwb221227
  • hwb221227
    hwb221227 Member Posts: 14
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    At the beginning of this saga I replaced all of the air vents in the system (a week ago). A day or two ago I drained the boiler (kept zones filled but isolated) and re-inflated the expansion the tank to 15PSI (it was maybe 8PSI when I measured it).