Air bound ???

Weezbo · November 2006

do you have a boiler or system by pass? are the settings on the aquastat zooming way up and way down? is this something that is zoned sans regard to velocity in the pipe?

if your pump is cavitating,hot as Hannah, banging into the zone at highest heat available...you got what you got.

You got Heat!

my thought rolls this way, dial the aquastat down a notch put one variable speed temp controler circ, by pass, something.... to allow the flow of the pump to maintain the sane. otherwise you are hammering the system with beaucoup heat ,the pump racing away ,the boiler in Shock and AWE of you the installer.... because it is acting just as an over sized boiler would behave sans doubt.

Brian Maffioli · November 2006

Air Bound???

Just got done replacing old steam boiler with new hot water boiler, keeping two sections of cast iron baseboard and two small rad's on 1st fl. purged system and rad's and all rad's became smoking hot until over night when it seems the homeowner would turn down thermostat at bed time and wake up to no heat. I went back to purge got super heat, same thing happened over next night. am i just not purging enough? Please help.

Steverino · November 2006

Brian

Not sure what you have as far as line size, but are you sure you have enough pump to move the water in those larger lines. (If SO) I guess that was a Question. Did you use Pri/Sec set up? More info needed. House size or EDR on radiators? Size of new boiler? Ya know the drill.

Mike T.

Timco · November 2006

Steamhead wrote a great article in the tech topics on how circs on converted gravity systems with large pipes are typically oversized due to very little head. I find a 15-58 will move a ton of water through those big pipes. Be sure to use a good air eliminator (Honeywell supervent is my fav) and pump away from the expansion tank. Install a purge station for the main (pri) and all zones, and purge well, then bleed from bottom up after running the circs for a few minutes. Vent should go just after the supply leaves the boiler to pull the most air out of the water.

Tim

Brian Maffioli · November 2006

Mike this boiler was set up originally to serve 2 zones of slant fin 30. at the last minute because of the home owners job moving to london they decided to get out of the job as cheeply as they could and keep existing rad's.
Thought I needed to get that out there, so any way the boiler is 120,000 btu and I ran 11/4 supply and return headers with 3/4 outlets. Now I only have the first floor heated (Waiting on homeowners and G.C. to decide on means of heating second floor) and a seperate zone for D.H.W.
Each of theese zones have their own taco 007 I.F.C.

I also have to say that off my supply I reduced from 3/4 copper to 1/2" pex until i reach my 1st piece of castiron base board then it increases to 3/4 again, then between the next piece of baseboard and the small rad's I have 1/2 pex jumpers I wouldent think that this could be the problem could it?

brucewo1b · November 2006

I would think it could

First rad gets hot but as you continue on the next rad gets less hot and so on until cool at the last plus you are probably not getting the flow through the 1/2 in pex you need. If it was home run to each rad it would probably work or moniflow with 1 or 1 1/4 pipe and 1/2 nch to each rad and back to the loop and are you pumping away if circ is on the return with pex adapters could cause enough restriction to create low pressusre and air coming out of solution.

Brian Maffioli · November 2006

NO problem with rad's getting hot. they all get so hot that I cant touch them. Its what happens after the thermostat is satisfied, seems to become air bound then because the next time the t-stat calls they get no heat, Then I get the call and have to re purge and the cycle starts all over again

brucewo1b · November 2006

Circ on supply or return

Brian Maffioli · November 2006

All circs are pumping away from boiler

Timco · November 2006

But are they pumping away from the expansion tank? That is the important part. sounds like you have a lot of suspended air that is setteling up when the system shuts down, and binds it up. GOOD purge, pump away from the x-tank, and good air removal devise.

Tim

Brian Maffioli · November 2006

air bound

Tim, My pumps are on the supply, after the scoop and expansion tank, I think you are right about a good purge,the problem is after a purge it gets smoking hot and the cast iron retains heat so well that it takes hours,sometimes a full day for them to become cool and then the home owner calls me with no heat. So am I just not purging well enough, and how can I tell when it is enough. not like purging a zone of slant-fin thats for sure

Timco · November 2006

I like to vamp the pressure to 29# and with the fill on, just as the prerssure reaches 29#, open the purge cock and let 'er run. (of course with the ball valve past the purge cock closed. As this happens, you will hear / feel air rushing out the hose. If you close the pruge cock 1/4 turn, this usually magnifies the flow sound, and you can really hear the air bubbles flying past. I then close the cock while continueing to fill and build back to 29# and try again. You will notice the needle on the gauge takes longer and longer to get to 29# as the air escapes. I do this cold, and bleed the rads hot. If flux / small debris has accumulated on the brush of the supervent, you may need to flush system with tsp or pull the top & bottom off the vent and I just hit the brush element with a little mapp gas...just to burn off the flux. The air really sticks to it then!

Tim

Brian Maffioli · November 2006

I actually did that last night. I brought the pressure in the boiler up to almost 30# and then opend my purge cock, although I did not try the partially closed trick. anyways once again it was hot, so mabey it has stayed that way.
But back me up, I think im on the right track with the air, not a pump or piping problem, right?

Leo · November 2006

The question is

Are you getting air each time? You also said there are cast iron radiators on the system. Are you purging all the air from the basement or have you blead the individual radiators also? Try doing the rads then going to the basement.

Leo

Timco · November 2006

It sounds like air is being sandwiched between the 1/2" in the 3/4, or something like that. Does the needle jump to 26-28# or rise slowly? I agree that it seems like air, and not a circ. I sometimes put the circ on high (grund 15-58) and close the iso flange quickly. This makes a velocity sound to ensure the circ is fine.

Tim

Air bound ???

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