Cannot get air out of hot water heating system

mulbill

Hello,

I have a hot water heating system that I had to open up to fix a leak and now I cannot get the air out of the system. My system is from 1953 and appears to be mostly original. It is only one zone and my house is a rambler with a basement. The furnace is in the basement.

Here is what I have been doing that doesn't seem to be working. I turned off the system. Let it cool down. I closed the valve on the return line right before it goes into the furnace, I closed the valve to the expansion tank, I opened the feed gateway valve and then opened the drain valve that is located on the return line right above the valve I closed that closes and opens the return line. I have a hose hooked to the drain valve with the other end in a bucket of water. I would turn the feed valve up until I have about 28 psi. I will let it drain like this for about an hour. There would be lots of air at first then a few bubbles and then finally no bubbles at all the bucket. A strong stream of water is coming out of the hose. I then would close the drain valve and then close the feed valve. I will then open the drain valve again to get down to about 15 psi.

I would then turn the system back on and the pipes are still so full of air I can hear it at the furnace and at most of the radiators instantly like it was a system that needed to be bled. Some radiators are not even getting warm.

How can there still be so much air in my system when there is no more bubbles coming out of my hose? My relief valve opens at about 40 psi. Do I need to increase the PSI during bleeding??

Thank you for any advice.

neilc

it might be that simple,
valve manipulations around the purge points differ system to system,

can you post pictures of your drain hose, the boiler, circulator, and pipes,
all in 1 or 2 shots so we can see what you're looking at?

also post a radiator or 2, standing rads or baseboard?
any venting upstairs at the rads?

HVACNUT

Yes, need pics of the boiler and piping from about 10 ft away.

Does the supply pipe go directly to the first radiator, or is there a perimeter loop in the basement and branch loops to each radiator?
If there's a perimeter loop, then you have a mono flo system and each radiator must be bled separately. 

mulbill

Sorry for the bad pics, there is only a couple of feet of space in front of the furnace so I cannot get one picture that has everything. There are several plumbing pipes that have nothing to do with the furnace that are right above the furnace so it is probably hard to tell what is what. The pipe with the green hose on it is the return line. The out of the furnace pipe is to the far right of the picture. The smaller pipe between the return and heat out line is the water fill pipe. From what I can tell the heated water goes straight up and then hits a T. One line of the T feeds the baseboard radiators on the front of the house and the other side of the T feeds the back. They meet at the other side of the house and then return in one pipe down the center of the house and back into the furnace. About half of the baseboards have bleeder valves. I have tried to bleed from those but just a small amount of air comes out each time I open them. It did not really seam like I was getting anything done bleeding at the radiator. The radiators farthest from the furnace and toward the back of the house were hot, but the farthest radiators toward the front of the house were barely warm.

neilc

after the supply tee's, or before the returns tee back to the common return,
are there any valves, balancing valves?
how to balance between front and back of house ?
you would need to isolate front from back while purging.

" I have tried to bleed from those but just a small amount of air comes out each time I open them"
is there an auto feed pressure reducing valve?
or is someone manually feeding and maintaining boiler pressure while you're bleeding rads?

actually, while bleeding at the rads, take advantage of the compression tank reserve pressure, leave its isolation valve open, may as well have it open while purging also,
but you need a way to isolate front and back of the house.

EdTheHeaterMan

It appears that you have 2 loops on one zone. The RED lines on the photo indicate the Supply pipe. It appears that it splits two ways just above the boiler. When purging, the water will take the path of least resistance. That path may be LOOP B and that air will purge. The other LOOP A may be be a little more restrictive. That loop will not purge unless you turn off a valve to stop the water from flowing thru LOOP B.

In order to get all the air to move DOWN a pipe, you will need sufficient velocity. If you fill the system with 28 PSI, including the expansion tank, that will help you entrain the air and move it DOWN that return pipe with the drain valve with the hose connected. If water just trickles with only 10 to 12 PSI behind it, chances are the air bubbles will just rise to the top of that pipe. When that air pocket reaches the circulator pump, there will be no water moving.


So... Two things:

• More water pressure with the expansion tank included
  
• Block each half of the system by closing a valve on the loop you are not purging. Then reverse the valves to purge the other loop
  

HVACNUT

Follow the return back and see if there's isolation valves on the split return. If so, close one valve, purge, the do the other. If no isolation valves, pipe them in.

mulbill

Thank you so much to all that have responded. This all makes so much more sense now.

I thought I was going to have to break out the pipe cutters because I don't remember seeing any valves anywhere but I took another look and found what you see in the picture. This picture is from the opposite end of the house where I believe the two loops come back together. Are those two fittings valves? The pipe in the middle is what I believe to be the return pipe. There appears to be a stem sticking out on each of those fittings that I could put an open end wrench on. Can I turn one clockwise and close the loop then purge and then rinse and repeat for the other loop? To the left off the picture I seem to have a loop within a loop which looks like that one will not be easy to purge.

Thank you again for all your help.

neilc

those are your valves, good find,
now, can you turn them?

that larger nut is a packing, loosening that packing just a bit, if they will go, should free up the valve stem,
start spraying them down with penetrating oils,
see if you can clean some of that old paint away from the threads first,

if when done purging, you still find one half of the house is cooler than the other, (imbalanced), choke down the hotter loop just a bit, till you find your balance

HVACNUT

mulbill said:

Thank you so much to all that have responded. This all makes so much more sense now. I thought I was going to have to break out the pipe cutters because I don't remember seeing any valves anywhere but I took another look and found what you see in the picture. This picture is from the opposite end of the house where I believe the two loops come back together. Are those two fittings valves? The pipe in the middle is what I believe to be the return pipe. There appears to be a stem sticking out on each of those fittings that I could put an open end wrench on. Can I turn one clockwise and close the loop then purge and then rinse and repeat for the other loop? To the left off the picture I seem to have a loop within a loop which looks like that one will not be easy to purge. Thank you again for all your help.

Nice! Those look like 1/4 turn valves. Right now the stubs are parallel (open) with the pipe. Turn 90° to close. 

mulbill

The valves turned easily but purging one loop at a time didn't seem to work any better than purging both loops at the same time. There is still air in the pipes and the back half of the house is not getting any hot water at all now. I can only hope that the valves don't open and close like I think they do. I don't have time to work on this today, but tomorrow I will experiment with the valves to make sure what I think is open and closed is actually open and closed.

leonz

mulbill said:

Sorry for the bad pics, there is only a couple of feet of space in front of the furnace so I cannot get one picture that has everything. There are several plumbing pipes that have nothing to do with the furnace that are right above the furnace so it is probably hard to tell what is what. The pipe with the green hose on it is the return line. The out of the furnace pipe is to the far right of the picture. The smaller pipe between the return and heat out line is the water fill pipe. From what I can tell the heated water goes straight up and then hits a T. One line of the T feeds the baseboard radiators on the front of the house and the other side of the T feeds the back. They meet at the other side of the house and then return in one pipe down the center of the house and back into the furnace. About half of the baseboards have bleeder valves. I have tried to bleed from those but just a small amount of air comes out each time I open them. It did not really seam like I was getting anything done bleeding at the radiator. The radiators farthest from the furnace and toward the back of the house were hot, but the farthest radiators toward the front of the house were barely warm.

=================================================================





OK here we go;


You have hot water boiler and a steel compression tank that is painted black and a Maine Coon Cat for a plumbers helper? I had 2 female Maine Coon Cat babies that lived to old age.

The steel compression tank works differently than a bladder expansion tank and has more water volume.

The red valve under the steel compression tank is a Bell & Gossett Airtrol valve.

The Airtrol valve allows the air bubbles in your system to exit the boiler and rise into the pipe connected to the Airtrol valve and be absorbed in the water in the steel compression tank.

The Airtrol valve has a drain valve in the base of the valve the allows excess to be drained from the steel compression tank to achieve the correct air to water ratio in the steel compression tank to create the point of no pressure change so that your circulator will work properly.

It sounds as if the root of all your trouble is the steel compression tank is waterlogged and needs to be drained correctly to create the correct ratio of water to air.

NOW; shut the boiler off please;

1. please shut off the blue handled globe valve under the steel compression tank just hand tight.

2. (a) open the drain valve under the Airtrol valve, by doing this it will allow the excess water in the tank to drain out and create the correct air(1/3) to water(2/3) ratio in the steel compression tank to create the point of no pressure change.
I do not remember if the brass drain valve is 5/16" or 3/8" as I have not had to deal with a water logged tank in many years.

3. after the correct amount of water has been drained from the steel compression tank air will begin hissing from the tank, now you need to close the drain valve on the Airtrol valve.

4. open the blue handled globe valve under the steel compression tank and then turn the boiler back on and turn the thermostat way up in the home and you will have a warmer home in a little bit as the air bubbles will rise from the boiler into the airtrol valve and the cool water in the tank will fall back into the system to replace the air bubbles.

Once you have very hot water in the baseboard loops in a couple of hours you can turn the thermostat back down; I hate hydronic baseboard because it has less thermal mass.

You will have a warm home and a cat that wants to hog all the baseboard in the house because it is hot.

Once you have the excess water drained out of the steel compression tank you will not have to mess with anything and you will have heat every year.

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Happy heating.

mulbill

Hello,

Thank you for the additional information. Yes, my helper is a Maine Coon who has lots of enthusiasm but not many skills. I did learn that the two valves I had do not shut off my loops...they seem to just slow the flow. Therefore I am glad to learn we could try to remove air at the tank.

I opened the valve as instructed. Only air and a little water came out. I just let the air come out until it stopped. I closed the valve back up and turned the furnace up a few degrees hotter than normal. Much of the air seems to have been removed from the system. It was hard to hear any air in the pipes and all the radiators appeared to get warm. I decided to open the air valve on the expansion tank again the next morning. This time water came out. To speed things along I opened the globe valve on the water tank and took out water until I could hear a lot of air coming out with the water. I guess there should be some water in the tank so I didn't remove it all. I opened the air valve again and this time just some air came out and little to no water, I closed the valve after it sounded like most of the air had come out. 10 hours later the furnace seems to be still running well.

I still seem to have one problem, which is the system has too much pressure. It is close to 30 psi. I believe it should be around 12 to 15. I open the main drain for a moment when the pressure seems to be too high but I am not sure how to get things back down to 12 psi.

Thank you very much to all that helped me.

OldawgBryant

@mulbill that tank needs water to balance the pressure, if there is more air than water, then it can't balance the pressure you may have emptied the tank too much, I think.
notice the previous instructions: "3. after the correct amount of water has been drained from the steel compression tank air will begin hissing from the tank, now you need to close the drain valve on the Airtrol valve. "

leonz

Hello mulbill,

You need to reopen those white valves more to allow the water and air bubbles to flow more freely to allow the air bubbles to be scrubbed from the system. Do not open them all the way as you could damage the valve stems.

Did you reopen the blue handled globe valve when you stopped draining air from the steel compression tank and restarted the boiler?? This valve HAS to stay open all the time when the boiler is running to allow the air bubbles to rise and the cool water in the steel compression tank to fall back to the boiler to provide system balance and maintain the point of no pressure change.

The rule for steel compression tanks is 1/3 air volume; 2/3 water volume.

If you are still having a heat issue you may have to start over again and have your faithful Maine Coone assistant close at hand to pass the box end wrench to you to bleed air from the steel compression tank and to take notes.

No worries, I will try to avoid stepping on my tongue while yapping, and collectively we the fine members of the forum get you there to a very warm home and a Maine Coone Cat that will always use the squirt bottle on you to keep you away from the baseboard heaters.

mulbill

Hello, Thanks for checking back.

Yes the white valves are open, I have the flats of the stems parallel to the pipes...so at least I think they are open...even what I believe to be closed they don't stop the flow of water.

Yes, the globe valve to the compression tank is open when the furnace is running and when I am not messing with the tank for that matter.

Yesterday morning and yesterday evening I closed the valve to the compression tank, opened the valve on the air valve and let water out until I got just air coming out. I let some of the air out because I think the problem is too much air in the system that heats and expands. I closed the air valve and opened the valve to the compression tank and let the furnace run as needed. It is somewhat cold here yesterday and overnight so the furnace is kicking in. When I checked on it yesterday afternoon after letting water and air out in the morning the pressure was about 35 psi. So that is why I went through the draining process again last night. After letting water and air out of the tank again last night the pressure dropped to about 18 psi. I checked the pressure a little while later after the furnace had been running and it was still about 18 psi. This morning I went to check on it again and it was at 40 psi and the relief valve had opened and sprayed water again.

I don't hear air in the pipes anymore so I don't understand where this pressure keeps coming from. It seems fine, but if you go check it 10 hours later the pressure is sky high again. This has been going on the whole time I had air in the pipes and I thought this was just a symptom of the air in the pipes, but the air seems to be gone. Any help would be appreciated.

neilc

I think it's time for another tank do over,
post a picture of the tank showing both ends all in one shot,
or, is that blue handled hose bib piped to the tank end?

you need to drain the tank, ONCE, let it refill, then leave it alone,
If you want to adjust pressures, either fill as you know how, or drain from a boiler drain, purge point, NOT THE TANK.
STOP touching the tank drain or airtrol, set them once and forget them.

isolate the tank,
attach a hose to the hose bib drain on the tank and open that drain,
let the hose go til it starts glugging,
at the airtrol, open the air inlet, you may or may not get a little water,
what you're looking for is for that air inlet to let air into the tank, the hose should start draining again,
walk away, let the tank drain, 5, 10, 15 minutes, what ever it takes to get to the point that the hose stops draining, and the air inlet stops letting air in,
Close the hose bib, and disconnect the hose, you're done there,

I think airtrol instructions says to open the isolation and let the tank refill til water comes from the airtrol air vent stem, these same instructions also say the stem needs to be fit to the proper height in tank.

I would just open the isolation and count to 5, and shut the airvent,

then leave it alone.

you let the air cushion out when you messed with the airtrol and water and air coming from it, don't do that.

jesmed1

I'm wondering if someone put the wrong size Airtrol on the tank. The Airtrols have different air tube lengths for different tank sizes, and if someone put an Airtrol with too long an air tube on your tank, and you then use the Airtrol to set the water level, you'll end up with too much water and too little air in the expansion tank, resulting in high pressures when the boiler runs.

I just installed an ATF-12 on our 14" diameter tank. The ATF-12 is correct for tanks 12"-14" diameter. Check the model number plate on the Airtrol and measure your tank diameter, and make sure the Airtrol is the right one for your tank size.

mulbill

Yes there is a blue handle drain globe valve at one of the tank. Yesterday I was draining water out of the tank through the air valve because the pressure went way up again. It seemed to be taking a long time so I thought I would open the tank drain to speed things up. Nothing came out. I opened the air valve and just a few drops of water came out. I concluded that if you open the air valve until water stops coming out the tank is nearly totally empty of water.

Looks like I need to add water to the tank, but I cannot get the air that is in there out so that will just compress and build up pressure. Not to mention I have no idea when the tank is 2/3 full of water. Also the fill, fills the whole system not just the tank, so how do you fill the tank without adding pressure to the whole system?? How does the air get out of the tank??

jesmed1

mulbill said:

Looks like I need to add water to the tank, but I cannot get the air that is in there out so that will just compress and build up pressure. Not to mention I have no idea when the tank is 2/3 full of water. Also the fill, fills the whole system not just the tank, so how do you fill the tank without adding pressure to the whole system?? How does the air get out of the tank??

The Airtrol fitting is designed to set the water level correctly, if you follow the instructions. Check the number on your Airtrol and make sure it's the right one. If you have a 12-14 inch diameter tank, it should be an ATF-12. If it's a smaller tank, an ATF-12 is not the right one.

Also, you WANT some air in the expansion tank. You WANT it 1/3 air and 2/3 water. That will happen if you (1) start with the tank empty of water and full of air at atmospheric pressure, and (2) fill it per the Airtrol instructions. When you do that, you will end up with 1/3 air and 2/3 water in the tank.

jesmed1

mulbill said:

I opened the air valve and just a few drops of water came out. I concluded that if you open the air valve until water stops coming out the tank is nearly totally empty of water.

That's not correct. The Airtrol has an air vent tube that sticks up into the tank about 8 inches or so. When you open the Airtrol bleed screw, whatever comes out is coming from that 8-inch height. If no water comes out, that only means that the water level is below 8 inches or so. It doesn't mean the water level is zero.

The only way you know the water level is zero is if you open the tank drain valve and no water comes out. Then the tank is truly empty.

Watch this video to see how the Airtrol works, starting at about 3:00:

https://youtube.com/watch?v=wzMS5p0MMv4

mulbill

Update,

So last night I isolated the expansion tank and pretty much emptied it with the airtrol vent open through the tank drain (sorry I was wrong before I could have sworn I opened the tank drain after draining through the airtrol and nothing came out which made me conclude their is no drip tube...I was clearly wrong) I could feel it sucking in air while it emptied and no water was coming out of the airtrol. By the way I have a 12 inch tank and a 12 airtrol vavle. I then opened the valve to expose the tank to the rest of the system which was at about 13 psi. I then turned the fill valve on and the tank started to fill. I could feel air being pushed out through the airtrol as it filled. It filled for several minutes and then water started dripping out of the airtrol. I then isolated the tank and just left the airtrol open until no more water or air was coming out of it. I believe the air in the tank is to start at atmospheric pressure and when no more water comes out it is at the correct water level. I then closed the airtrol and opened the valve back up to expose the tank to the rest of the system. The whole thing was still at about 13 psi and the furnace pipes were almost lukewarm to the touch. It was a warm day here so the furnace had not run in a while.

This morning the furnace was running and the temperature of the return was around 170 degrees. I don't remember ever seeing it that hot but I am not constantly checking so maybe it is sometimes. The pressure had increased to around 28 psi. All the radiators felt very warm and I didn't hear any air or bubbles in the system. I have lived here 14 yrs and I believe other than the high pressure this seems like this is the best this thing has ever run. I opened a drain just above the circulater pump and let water out after the furnace had stopped running and brought the pressure down to 20 psi.

Does anybody have any ideas on how to lower the pressure? I believe even when hot it should only be around 12 to 15 psi. I am afraid I will let too much air in the system if I leave the purge valve open to drain out more water, but maybe that is how it is done?

Thank you to everyone who has contributed I don't think I could have gotten this far without you.

jesmed1

mulbill said:

Does anybody have any ideas on how to lower the pressure? I believe even when hot it should only be around 12 to 15 psi. I am afraid I will let too much air in the system if I leave the purge valve open to drain out more water, but maybe that is how it is done?

You did fill the tank *almost* exactly per the Airtrol instructions. The one thing you did that is *not* in the Airtrol instructions is that, when water started coming out of the Airtrol vent, you briefly stopped filling and allowed more air to come out of the vent before you closed it and resumed filling. That resulted in less air in the tank, and more water, which is still your problem. You want MORE air and LESS water.

Note that you CANNOT fix the problem by simply now draining water out of the Airtrol vent, because as the water level in the tank drops, the air in the tank will expand and its pressure will drop. Then when you open the tank isolation valve, water will flow back into the tank against the lower air pressure until it equilibrates, again at a higher water level.

The correct way to reset the water level is to start with an EMPTY tank, and fill it just like you did before, EXCEPT don't stop to let excess air pressure bleed out of the Airtrol vent midway through filling. Just close the vent after water starts streaming out, and KEEP FILLING. Then you'll end up with less water and more air in the tank, which is what you need.

And if you still experience high pressure swings after that, the next step would be to drain the tank and refill it from empty, but don't use the Airtrol at all. Keep the AIrtrol vent closed and do not let ANY air out while filling. That will result in your tank being 1/2 full or less, giving you maximum free volume for water expansion. (If you do that, make sure you start with the system dead cold, because you want to make sure the water level doesn't drop any lower when the warm water in the system cools off.)

Once you get MORE air into the tank and LESS water, your pressure spike will reduce. Your problem continues to be too much water and not enough air in the tank.

neilc

that poor tank, would you leave it alone , , ,
#kidding,
I think you're ok at the tank,

shut off your water feed to your boiler,
your pressure reducing valve is either leaking by, or adjusted too high,
shut off a ball valve to isolate the boiler system from the feed.
then from that picture with the hose over the circulator,
let some water out til the pressure is down where you want it,
12, 15 tops,
keep the feed to the boiler shut off until you see the need for more pressure.

Your domestic hot is not part of the boiler, is it?
either as an indirect, or,
is there any piping between the boiler and the domestic hot tank other than the cold water supply?

mulbill

Hello,

Sorry it took me so long to check back. My furnace in question is only for heating. I totally emptied the tank again and closed the Airtrol before adding any water. The furnace was cold at this point. I only have a manual feed and I turned it on a little bit for just a few seconds. Again the furnace seemed to work fine for a week but the pressure started to build again until I had another blow out through the relief valve.

I wasn't sure what to do at this point, but I thought the pressurized air must being adding to the pressure so when the system was hot I let air out through the Airtrol. Lots of air came out, it was liking emptying an air compressor at the end some steam came out too. I believe I left it open until nothing else came out. I closed the valve at that point. The pressure dropped but not very much. So at this point I opened the purge valve and let water out. I just let it run until the pressure dropped down to about 18 pounds. It seemed like the pressure dropped alot at first but then I got to this point where the water was still coming out but the pressure drop slowed down.

At this point I restarted the furnace but the front of house loop was stone cold. I assume I let too much air in and the front loop was vapor locked. I let out some air at the registers until some water showed up. The back loop seemed to have heated up fine. I left it like this for the day.

While at work the furnace gods visited my house because when I got back both the front and back loops were nice and warm. Also, the furnace/radiators make no sound to indicate there is air in the pipes. The pressure is holding after several days of cycles at about 20 psi. I thought I might be low on water after letting all the water out to bring the pressure down but even though the guage read 20 psi the preassure relief valve would open the second I opened the fill valve so I just gave up on that. So unless something changes I am not going to make any adjustments. I have no idea why this works. I have also lived here for 14 years and have never experienced anything like this before. Generally at the beginning of each heating season and maybe one time during the winter I would add a random amount of water and the pressure never changed much. It makes no sense to me why this was so hard to bring the pressure down and I don't understand why it seems to work now. Maybe I needed all the air in the tank plus some air in the pipes???

neilc

maybe the boiler gage is bad,
get a hose end connection and gage, connect to a bib,
stop playing with the tank,