Tricks to bleeding a problem radiator?
When I started taking responsibility for maintenance in the building, I found that previous owners had not bled any radiators in any of the 4 units for years, leaving the system half-functional and full of air. This particular radiator was so air-bound that we had to call our oil company. The tech came with a 5-gallon bucket and had to bleed it half full to get all the air out. That was 2-3 years ago. Since then, I have encouraged the owner of that unit to bleed her radiators every year, in the fall after the boiler tech comes and does his annual boiler cleaning, and purge/fill of the old non-bladder-type expansion tank.
Yes, I know we need to get modern diaphragm-type expansion tanks and automatic air eliminators. But until that happens, we're stuck bleeding radiators manually. And the owner of this particular unit seems to be having a hard time getting the air out of her radiator again.
I've given her a 2-gallon bucket and asked her to bleed at least a gallon of water into it, and hopefully that will get the air out. But so far, she hasn't been able to get the air out.
Are there any tricks that I can share with her for getting the air out?
Thanks.
Comments
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there is nothing wrong with the old type tanks,
IF,
they're piped correctly, and the circ(s) pump away from them,
you may just have air trapped up in the building still,
post a pic or 2 of the boiler, circ(s), and tank,
all in one shot, from a couple angles, floor to ceiling,
sometimes it's better to bleed rads when circs are turned off,
you'll also know you have the correct pressure up there, instead of being fooled by circulator pressure ,
how many floors?
and what's the fill pressure?known to beat dead horses
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Air will collect at the highest point in the system. If that point does not have enough flow (velosity) the air will stay there and not be returned to the boiler and then into the non-bladder expansion tank.
In addition (and some do not know this) make sure there are no automatic air vents in the system. They will vent air out and cause the expansion tank to get waterlogged.
Raising the pressure temporally will make the system easier to bleed.
I don't know if the radiation has valves in the tenant space. If it does closing one valve and then bleeding may help.0 -
Thanks. This system was piped 100 years old by the Dead Men, so it was done right as a gravity system. Circulators were added later, at a time when the importance of "pumping away" from the tank wasn't understood, and there's nothing I can do about circulator location in the short term. @EdTheHeaterMan has seen pics and has observed that there are no bypass valves, but that's a different problem.neilc said:there is nothing wrong with the old type tanks,
IF,
they're piped correctly, and the circ(s) pump away from them,
you may just have air trapped up in the building still,
post a pic or 2 of the boiler, circ(s), and tank,
all in one shot, from a couple angles, floor to ceiling,
sometimes it's better to bleed rads when circs are turned off,
you'll also know you have the correct pressure up there, instead of being fooled by circulator pressure ,
how many floors?
and what's the fill pressure?
Otherwise everything is correct as far as piping goes. I have upped the pressure to 20 psi (in a 2-story building with boilers in the basement) to try to get the air out, but so far this one radiator won't cooperate. And we always bleed with circs off and the system cold.0 -
Yes, this is probably a velocity problem. The supply and return pipes are probably too small, and several other first-floor radiators branch off at the same place, so the circulator is forcing most of the flow to short-circuit through the first floor rads there.EBEBRATT-Ed said:Air will collect at the highest point in the system. If that point does not have enough flow (velosity) the air will stay there and not be returned to the boiler and then into the non-bladder expansion tank.
In addition (and some do not know this) make sure there are no automatic air vents in the system. They will vent air out and cause the expansion tank to get waterlogged.
Raising the pressure temporally will make the system easier to bleed.
I don't know if the radiation has valves in the tenant space. If it does closing one valve and then bleeding may help.
I am sure there are no automatic air vents. We never have a problem with waterlogging the tanks. I have raised the pressure to 20 psi, and still no joy.
There is one valve on the return. I'll ask her to close it, and hopefully that will do it.0 -
@DanHolohan had a great way of explaining why a system installed like @jesmed1 would have air problems and how the air found its way out of an expansion tank into the radiators.
You need to understand Boyle's law and Henry's law on dissolved air in water. He went into those laws of physics in some detail without getting too technical. Let it suffice to say that air is dissolved in water, and the ability of water to hold dissolved air, depends on pressure and temperature. Since the circulator pump causes a difference in pressure and the flame causes a difference in temperature, understanding those laws will help you understand how this all happens.
A closed expansion tank without a diaphragm or bladder, allows the air and the water to be in direct contact. That allows water and air molecules to interact at the water’s surface.
Cooler water can hold more air than warmer water. So if by chance the water in the tank has less dissolved air in it that it can handle, then that water will try to absorb some air from the air cushion at the top of the tank.
Lets say that the expansion tank is connected to the supply pipe of the boiler as it makes a turn into the main trunk line of the system. If there is no Airtrol fitting on that expansion tank then heated water in the supply pipe might find its way to that pipe to the expansion tank. If it is hot enough, a small amount of that heated water may find its way rising up that pipe and at the same time some of the colder heavier water in the tank may find its way moving down that same pipe. (in another portion of the class we learn about ghost flow where this can cause a radiator to get warm or hot, even if the pump for that zone is off)
So in the pipe some cold water is dropping and hot water rising until eventually the expansion tank is quite warm setting there between the rafters of the basement
Think about how much dissolved air might have been in that cold water that left the tank. As soon as that cold water got mixed in with the hot supply water, WHAM the dissolved air gets released in the form of tiny microbubbles, because that heated water can no longer hold that air in suspension.
Now think about that heated water that found its way into the expansion tank. It was hotter, so it contained less dissolved air. What happens when that water cools down in the expansion tank later on. It is in contact with the air in the tank and can absorb more air. Later that evening, the heater runs again and the same thing happens. Weeks go by, even months, but eventually that expansion tank becomes waterlogged as the air leaves the tank one molecule at a time getting absorbed into the expansion tank water.
Where does all that air from the expansion tank end up? In the radiators somewhere. And what happens when you get air in the radiators?, you bleed them to get the air out. And what replaces the air that leaves the radiator? More water because that is how you add pressure to the boiler to get the air out…
How do you solve this problem? Pumping away from the expansion tank on the supply side of the boiler. You place a micro-bubble air separator and the expansion tank at the lowest pressure highest temperature location in the system. With a bladder tank you just vent the air with an auto air vent. On a regular expansion tank, you pipe that air back to the expansion tank where it is supposed to be. Eventually that design will actually absorb air from the entire system and put it where it is needed.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Thank you, Ed. Trapped air is an ongoing headache with this system, so I'm hoping we can eventually replumb it with bladder tanks and air separators as you recommend.
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As I recall this was an old gravity system so with oversized pipe the velocity is slow.0
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Correct. Would it help if we changed out the Taco 007's for higher flow rate circulators? The limiting factor is the 1-1/4" copper pipe where all the old large-diameter pipes run into the boiler. I understand we could run into velocity noise problems, so maybe that is not a good idea.EBEBRATT-Ed said:As I recall this was an old gravity system so with oversized pipe the velocity is slow.
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Yes I think more flow would help0
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What circulator would you recommend?EBEBRATT-Ed said:Yes I think more flow would help
Our longest loop is about 100 feet, so I figure 6 feet of head, which would give us about 13 gpm based on the Taco 007 curve. The Bell & Gossett "Zoning Made Easy" pamphlet says 14 gpm is the max for our 1-1/4" copper at the boilers, but maybe we can safely ignore that since the copper runs are only 6 feet or so before they transition to the larger diameter steel/iron pipes.
A Taco 0010 would give us 20 gpm at 6 ft head, for example, for a 50% increase in flow rate. This multi-speed version might be good because we can select the speed and turn it down if necessary:
https://www.grainger.com/product/2KGX8?gucid=N:N:FPL:Free:GGL:CSM-1946:tew63h3:205012310 -
Is there any reason the system cannot be returned to a gravity system?????
As Mr. Holohan is fond of saying "if you have water coming out when bleeding a radiator it ain't an air problem".
In my case, I always raise the boiler temperature at the start of the heating season to remove any trapped air at the high points in my single loop system.
Perhaps all you really need to do is raise the water temperature in the system to purge the radiators of air?
I have a steel compression tank with a sight glass water gauge and it has worked as it should for the last 8 heating seasons.
If she closes the valve for that radiator all the way she will not have heat!!
A water fill valve should not be left on all the time with a steel compression tank system as it will waterlog.
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Well, that's an interesting question that I don't know enough to answer. But now that we have circulators installed, why go back to gravity?leonz said:Is there any reason the system cannot be returned to a gravity system?????
OK, thank you for the suggestion. I guess we could turn the thermostat up high for one cycle to get the radiators hotter than usual and bleed the air then. I didn't know that would help.leonz said:
In my case, I always raise the boiler temperature at the start of the heating season to remove any trapped air at the high points in my single loop system.
Perhaps all you really need to do is raise the water temperature in the system to purge the radiators of air?
I understand that's a possible pitfall, but I don't believe our tank ever gets waterlogged. It's a 40 gallon tank that gets drained every year. Based on our system pressure, it probably starts out around half full, so 20 gallons of water and 20 gallons of air. It seems unlikely to me that 20 gallons of air dissolve into our water every year. We don't ever get that much air out when we bleed radiators. And we never get discharge from the pressure relief valves, which would be happening if the tank was waterlogged.leonz said:
A water fill valve should not be left on all the time with a steel compression tank system as it will waterlog.0 -
jesmed1 said:
Well, that's an interesting question that I don't know enough to answer. But now that we have circulators installed, why go back to gravity?leonz said:Is there any reason the system cannot be returned to a gravity system?????
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Simplicity is why, there is no steel compression tank or circulators, the radiators are filled from the basement or the attic tank.
The open to air expansion tank is filled with water and any overflow will either be drained to a basement drain or a roof vent pipe to be drained into a rain gutter.
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OK, thank you for the suggestion. I guess we could turn the thermostat up high for one cycle to get the radiators hotter than usual and bleed the air then. I didn't know that would help.leonz said:
In my case, I always raise the boiler temperature at the start of the heating season to remove any trapped air at the high points in my single loop system.
Perhaps all you really need to do is raise the water temperature in the system to purge the radiators of air?
I understand that's a possible pitfall, but I don't believe our tank ever gets waterlogged. It's a 40 gallon tank that gets drained every year. Based on our system pressure, it probably starts out around half full, so 20 gallons of water and 20 gallons of air. It seems unlikely to me that 20 gallons of air dissolve into our water every year. We don't ever get that much air out when we bleed radiators. And we never get discharge from the pressure relief valves, which would be happening if the tank was waterlogged.leonz said:
A water fill valve should not be left on all the time with a steel compression tank system as it will waterlog.
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Once the system is filled the water fill valve HAS TO BE SHUT OFF.
The "ONLY" time you drain a steel compression tank is if it is waterlogged or need to do a repair that requires a total drain down of a system if there are no valves to stop water loss.
Does this 40 gallon steel compression tank have a sight glass??
Your tank does not require draining every year as the air charge/air blanket over the water in the tank will stay in the tank.
Whoever told you to drain it was mistaken in telling you this as it changes the balance of water and air in the entire system every time you drain it and fills with air and as a result more air gets in the radiators.
If you are draining 40 gallons of water out of this tank and your fill valve is shut off to begin with you have an ingress leak and you have a valve that not shut or leaking by.
Have you ever shut the boiler down and just let the water vent out of this top floor radiator for a couple of hours with a hose and then drained the steel compression tank of excess water and stopping when the airtrol valve is spitting air???
Please post more pictures of your system.
Can you post some pictures of your steel compression tank and the airtrol valve????
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I understand the logic for shutting the autofill off. But the flip side of the coin is that leaving the autofill ON is a safeguard against the boilers running out of water and getting damaged. Some people say turn it off, and some people say leave it on.leonz said:
Once the system is filled the water fill valve HAS TO BE SHUT OFF.
The "ONLY" time you drain a steel compression tank is if it is waterlogged or need to do a repair that requires a total drain down of a system if there are no valves to stop water loss.
As for draining the tank, the boiler techs do it every fall when they come to clean and service the boilers. It seems that's what their boss tells them to do. We have no say in it. Maybe we should just go ahead and install a diaphragm tank so they'll stop draining and filling it every year as a matter of routine.
No, there's no sight glass, so I have no idea of the water level. And there's no Airtrol fitting, just a Drain-O-Tank drain valve.0 -
I think a 3 speed 0010 would be a good choice. Your boilers output is 140000 so 14 gpm is a 20 degree TD. Your 007 is close to that but with the oversized pipe your velocity is low. I think the bigger pump will help.
The only other think to try is to possible throttle a few radiators the ones closest to the boiler might give you enough of an increase to the problem radiator. As you know the water will take the path of least resistance and the 007 looks like it may be slightly undersized. With the short 1 1/4 connection you can ignore that. Not enough there to cause any restriction.0 -
It is too bad the boiler service people don't know what they are doing.
With the steel compression tank water logged you have lost the point of pressure change and your circulator is not performing as is should and your wasting fuel.
Put a tag on the drain valve and tell them the steel compression is fine as is do not touch
it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
The water level in the steel compression tank is correct when the excess water in the tank can no longer
drain into the tiny copper drain pipe in the drain-o-tank valve and out of the boiler drain.
Again, the water has to be shut off; and then you open the drain-o-tank valve and leave it open until you no longer have water coming out of it and by then the water to air ratio is fine and the problem radiator should no longer be a problem after you open the radiator vent to purge it of air after you have drained the excess water from the steel compression tank.
Your leaving the water feed on is what causing your heating balance issues thus causing the loss of the point of pressure change.
With a gravity hot water heating system there is no point of pressure change as you are depending on hot water to rise to the top radiator and then drop back to the boiler as the water cools.
Why waste money on a bladder expansion tank and rip out good plumbing and add air vents that will leak, an air scoop, more fittings and pipe to install a bladder tank when it is not necessary??????????????????0 -
OK thanks Ed. That's a good idea too about throttling some neighboring radiators.EBEBRATT-Ed said:I think a 3 speed 0010 would be a good choice. Your boilers output is 140000 so 14 gpm is a 20 degree TD. Your 007 is close to that but with the oversized pipe your velocity is low. I think the bigger pump will help.
The only other think to try is to possible throttle a few radiators the ones closest to the boiler might give you enough of an increase to the problem radiator. As you know the water will take the path of least resistance and the 007 looks like it may be slightly undersized. With the short 1 1/4 connection you can ignore that. Not enough there to cause any restriction.
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OK, thank you. There's a lot of info in there, so let me make sure I understand:leonz said:Put a tag on the drain valve and tell them the steel compression is fine as is do not touch it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Again, the water has to be shut off; and then you open the drain-o-tank valve and leave it open until you no longer have water coming out of it and by then the water to air ratio is fine and the problem radiator should no longer be a problem after you open the radiator vent to purge it of air after you have drained the excess water from the steel compression tank.
Your leaving the water feed on is what causing your heating balance issues.
1. Never drain the expansion tank. OK, we can do that.
2. Shut off the auto-fill water feed. OK, we can do that. But please explain why you say "leaving the water feed on is what is causing your heating balance issues." IMO, what's causing our problem is that every year the tech drains probably 20 gallons of water from the expansion tank, then adds 20 gallons of air-containing water back in, and the air in our radiators is coming from that 20-gallon annual fresh water injection.
3. I don't understand what you're saying about draining the expansion tank partway. Are you saying to do that annually as routine service, instead of draining it completely? Or just do that once, and never touch it again? Because the Drain-O-Tank valve has an air bleed screw on it, and typically (I think) the tech opens the air bleed screw, then drains the tank entirely, closes the air bleed screw, and opens the auto-fill valve to let the tank recharge to system pressure. (I could be wrong, but I assumed the tech was always draining the tank fully. But I don't know; maybe he does it the way you say.)
4. If I do partially drain the expansion tank as you say, then turn the auto-fill off, doesn't the air in the expansion tank eventually dissolve into the water anyway, and still end up in our radiators?0 -
jesmed1 said:
OK, thank you. There's a lot of info in there, so let me make sure I understand:leonz said:Put a tag on the drain valve and tell them the steel compression is fine as is do not touch it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Again, the water has to be shut off; and then you open the drain-o-tank valve and leave it open until you no longer have water coming out of it and by then the water to air ratio is fine and the problem radiator should no longer be a problem after you open the radiator vent to purge it of air after you have drained the excess water from the steel compression tank.
Your leaving the water feed on is what causing your heating balance issues.
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1. Never drain the expansion tank. OK, we can do that.
GOOD
2. Shut off the auto-fill water feed. OK, we can do that. But please explain why you say "leaving the water feed on is what is causing your heating balance issues." IMO, what's causing our problem is that every year the tech drains probably 20 gallons of water from the expansion tank, then adds 20 gallons of air-containing water back in, and the air in our radiators is coming from that 20-gallon annual fresh water injection.
(2) no, once you have the tank properly drained it will have the correct ratio of water and air and they don't need to do anything to the tank NOR DO THEY need to touch it.
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3. I don't understand what you're saying about draining the expansion tank partway. That reduces pressure in the tank. Then when we open the isolation valve, the entire system is going to depressurize back into the expansion tank, and now the expansion tank is pressurized again. So what's the point? As long as there's an air cushion in the tank large enough to handle the expanded water volume, what does it matter whether the tank is 20% full or 50% full?
(3) the steel compression tank and the proper level of water is what makes the point of no pressure change for you because the water is pushing against the air blanket in the tank.
The drain-o-tank valve is designed to correctly drain the amount of water from the steel compression tank each time because of the copper drainage tubes length in the tank. when you have nothing but a tiny bit of water and more air coming out of the drain-o-tank valve that is when you shut it.0 -
That's not how the Drain-O-Tank instructions say to use the valve. The air bleed screw and tube are not intended to set a precise level of water in the tank. They exist only to allow air to flow easily into the tank while the tank is being drained. Then when the tank is fully drained, it says to close the air bleed screw and open the iso valve to allow the tank to refill with water. The air inside the tank will pressurize as water flows into the tank, until equilibrium is established. If the auto-fill regulator is set at 15 psi, that means the tank will fill roughly halfway with water. But the exact level of water doesn't matter, as long as there's sufficient free volume in the tank to accept the expanded water volume.leonz said:
(3) the steel compression tank and the proper level of water is what makes the point of no pressure change for you because the water is pushing against the air blanket in the tank.
The drain-o-tank valve is designed to correctly drain the amount of water from the steel compression tank each time because of the copper drainage tubes length in the tank. when you have nothing but a tiny bit of water and more air coming out of the drain-o-tank valve that is when you shut it.
Maybe you're saying that, in future years, when we're no longer draining the tank annually, we should use the air bleed screw as you say, to drain any excess water down to the level of the air inlet tube, and this way ensure that there is still sufficient air cushion in the tanks? If that's what you're saying, then I understand the logic.
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Is the galvanized pipe to copper pipe that is in the picture you were so kind in providing Tee'd into this tank???0
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Ah ok.0
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Since that system was Gravity, you do not need a different circulator. Taco 007 is fine. There is plenty of water flow thru those two systems, otherwise you would have higher boiler temperature at the supply and lower return temperature as a result of restriction.leonz said:It is too bad the boiler service people don't know what they are doing. How do you know this @leonz
With the steel compression tank water logged you have lost the point of pressure change and your circulator is not performing as is should and your wasting fuel. Not exactly true
Put a tag on the drain valve and tell them the steel compression is fine as is do not touch
it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I would not do this, There may be a histroy that we do not know about, this may end up with a waterlogged tank in a few years if left alone. The company that has serviced this location for years may have experience with waterlogged tank and have a note on the customer file that says DRAIN EXP. TNK. ANNUALLY. That may be why there is no waterlogged tank
The water level in the steel compression tank is correct when the excess water in the tank can no longer
drain into the tiny copper drain pipe in the drain-o-tank valve and out of the boiler drain. There is no Airtrol on the 1/2" pipe that leads to the boiler, and I can't tell if that boiler drain is a Drain-o-tank valve and your instruction on how it is used is incorrect. that tiny tube is to let air in when you drain the tank. Actual instructions here
Again, the water has to be shut offbetween the tank and the boiler system; and then you open the drain-o-tank valve and leave it open until you no longer have water coming out of it and by then the water to air ratio is fine and the problem radiator should no longer be a problem after you open the radiator vent to purge it of air after you have drained the excess water from the steel compression tank. Correct on the operation for the tank but I added 7 words to your instruction
Your leaving the water feed on is what causing your heating balance issues thus causing the loss of the point of pressure change. incorrect information. many auto feeds are left on and most of them are not having "balance issues"
With a gravity hot water heating system there is no point of pressure change as you are depending on hot water to rise to the top radiator and then drop back to the boiler as the water cools. You got that right
Why waste money on a bladder expansion tank and rip out good plumbing and add air vents that will leak, an air scoop, more fittings and pipe to install a bladder tank when it is not necessary?????????????????? Agree with this. Wait until you get other work done, then make the entire system correct at that time
The imbalance is perhaps from the air getting into the one or more of the radiators as a result of the phenomenon explained earlier https://forum.heatinghelp.com/discussion/comment/1767019#Comment_1767019
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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A closed steel expansion tank works properly when it is completely empty of water before you connect it to the system pressure (open the isolation valve on the connecting pipe). With a 40 gallon tank of air at zero PSI, when you add 15 PSI water pressure to the previously empty tank, it may take 30 to 34 gallons of water to compress the air until it reaches 15 PSI. You do not want to pre-water that tank to a certain level based on the size of a air vent tube of a drain-o-tank valve. You want to start empty of water to be sure you have enough air to compress.
That is the reason a 5 gallon Extrol #30 (that is approximate) can do the job of a 30 gallon steel tank. The amount of air in a 30 gallon steel tank takes up only about 4 to 5 gallons of space in that tank. Some egg head at Amtrol came up with that idea years ago, and tried it out just to see if it would work. Use a pre-charged 5 gallon tank in place of a 30 gallon tank. Guess what? It worked!
@jesmed1 Don't change a thing, there is no economic value or fuel savings by changing an expansion tank. But if for some reason you need to, because a tank starts to leak, you will need an Extrol #60 (or equal) for your system and if you ever put both systems together, You might need an Extrol #90 (or equal). (two 40 gallon tanks = one 80 gallon tank is the simple math I would use. Or you can use a water meter when you fill the system the first time after the new boiler is installed. Once you know exactly how much water it takes to fill the system then you cna size the tank according the the actual water volume.
100 gallons of 70°F water will be about 104 gallons of 230°F water so you want a compresses tank of air to have about 25 gallons of air space to compress so it can accept 4 gallons without changing the air pressure too much. Why so much... if you only had an 8 gallon air space at 15 PSI, when you added 4 gallons to that system you would use up 1/2 of that air space and that would increase the air pressure and water pressure in the boiler to 35 PSI... and that mean the 30 PSI relief valve would operate and blow about 4 gallons of water on the floor. that is what happens when the closed steel tank is waterlogged.Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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@EdTheHeaterMan OK, thanks Ed. I understand your math behind the tank sizing. And AFAIK, the boiler techs have indeed been fully draining the tank before refilling, to get the full air cushion as you describe.EdTheHeaterMan said:
@jesmed1 Don't change a thing, there is no economic value or fuel savings by changing an expansion tank. But if for some reason you need to, because a tank starts to leak, you will need an Extrol #60 (or equal) for your system and if you ever put both systems together, You might need an Extrol #90 (or equal). (two 40 gallon tanks = one 80 gallon tank is the simple math I would use. Or you can use a water meter when you fill the system the first time after the new boiler is installed. Once you know exactly how much water it takes to fill the system then you cna size the tank according the the actual water volume.
I will take your advice and wait until a boiler goes out before getting a new tank.
However, that leaves us with the ongoing problem of air in radiators which is proving very difficult to get out. In one unit the owner has bled gallons of water and still can't get the air out. And she doesn't want me in there messing around with it, so she's stuck with that cold radiator, and possibly some others.
So is there anything else I can do to minimize the air problem for now? Leonz pointed out that we have no Airtrol fitting on the tank. (We do have a fitting that has a bleed air screw to help tank drainage. See pic below. I don't know if it has any Airtrol-type flow control tubes inside.) I could remove that fitting and add an Airtrol tank fitting. However, we wouldn't have the corresponding Airtrol fitting on the boilers that scoops the air bubbles out and sends them off to the expansion tank. So I don't know if it's worth installing just the Airtrol tank fitting by itself.
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If you are opening a vent at the top of a radiator. and no air is coming out, then you do not have an air problem. You have a balancing problem. That may be fixable by opening and partially closing radiator valves. (or it could be a blockage problem that bleeding won't solve)
There is a story about a one pipe diverter tee system (not what you have) that had 2 radiators closest to the boiler return that never get heat. Of course if a radiator has air in it, we all know that it will not heat. So you bleed the air out of the radiator. but in this case no air comes out. So they keep bleating for 5 minutes of more hoping that there is some air bubble stuck on the bottom of the radiator (unlikely) that will eventually come out. After purging the radiator for that extended amount of time, eventually hot water from the boiler reached the radiator. Then you think THE PROBLEM IS FIXED because you got heat in the radiator. Tomorrow however, the same problem exists. Not an air problem, it is a design problem. see the illustration in the attached file.
As the water enters a radiator and gives off it's heat, and the colder water mixes with the 180° boiler supply water. The next radiator then gets the cooler water and that gives off its heat, and returns cooler water to mix with the hot supply water. This continues until there is not enough heat at the last radiator on the system. The fix for this system would have been to use a larger main pipe to carry more water volume so the temperature in the main pipe would not drop so much after each radiator.
In your system you need to find if there is a place where there is something blocking the heated water from getting to that radiator. The second illustration may be one reason. But this is only a guess, you (or the plumber) need to do the investigating. Look at the way the pipes run to the problem radiator. Even though it is not the farthest, it may be the direct path that air is taking and it there is an AIR TRAP. No amount of radiator bleeding will create enough velocity to move that air from the high point of a larger pipe.
Zoom in on the top left radiator and see how the air can get trapped from a pipe that has settled over the 50+ years it has been there. This is just one idea, there could be an actual blockage somewhere made up of all the rust from that Weil McLain boiler that isn't rusting away from the inside
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Actually you do have the needed boiler fitting. it is built in to the boiler. look at the tapping locations on the boiler. Tapping N is 1/2" and is higher in the boiler than the top 1-1/2" supply tapping C. This creates an air scoop at the hottest point in the system. this is where all the micro-bubbles will gather and find their way to the expansion tank.jesmed1 said:So is there anything else I can do to minimize the air problem for now? Leonz pointed out that we have no Airtrol fitting on the tank. (We do have a fitting that has a bleed air screw to help tank drainage. See pic below. I don't know if it has any Airtrol-type flow control tubes inside.) I could remove that fitting and add an Airtrol tank fitting. However, we wouldn't have the corresponding Airtrol fitting on the boilers that scoops the air bubbles out and sends them off to the expansion tank. So I don't know if it's worth installing just the Airtrol tank fitting by itself.
For extra insurance you can add an Airtrol tank fitting here.
Look at the attached files to see the difference when you use the tank fitting and when you don't use the tank fitting. there is a small baffle that causes a heat trap so the hotter water can't drop down, then go up, to find its way into the tank. If no hot water goes in then, no cold water can come out. Solving the water logged tank issue. IF YOU DO THIS, THEN PUT @leonz note about DO NOT DRAIN EXPANSION TANK because the air scoop and fitting are doing all the purging. You may even get more air in the tank than there would be after you drain it. Any air in the rest of the system may get absorbed in the water over time and find its way to the tank, with this setup.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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OK, thanks Ed. I have some history with this radiator. When I started digging into the problems with this system, I found the radiator was so air-bound that we had to call the oil company to come and bleed it professionally. The tech used a 5-gallon bucket and probably bled 2 gallons of water and 1 gallon of air out of it. Then it worked OK that winter. Next winter not so well. Now it's gone cold again and bleeding doesn't get any air.EdTheHeaterMan said:If you ate opening a vent at the top of a radiator. and no air is coming out, then you do not have an air problem. You have a balancing problem. That may be fixable by opening and partially closing radiator valves. (or it could be a blockage problem that bleeding won't solve...
There could be a number of other factors as you say. One is that this (second floor) radiator branches off with small diameter pipe in the same area where several other first-floor radiators branch off with larger pipe. So most of the flow is going through those first-floor radiators with the larger pipes. And this second-floor radiator with smaller pipes probably has little flow and little velocity.
I've checked the pipe pitches and they seem OK. No obvious air traps. There might be a clogging issue too as you said. But short of shutting off that branch and disconnecting some unions to try and blow/clean any blockage out, I don't think I can do anything. Maybe when that boiler gets replaced, I can try.
I do recall in Classic Hydronics that Dan said the old-timers would sometimes install orifices in the second-floor radiator valves to force more flow into the first-floor rads, in the days before circulators. So maybe when the system gets shut off/drained sometime, I could break open that valve and see if there's an orifice that's partially clogged.
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@EdTheHeaterMan Thank you for finding that! Seems like every day I learn something new here!EdTheHeaterMan said:
Actually you do have the needed boiler fitting. it is built in to the boiler. look at the tapping locations on the boiler. Tapping N is 1/2" and is higher in the boiler than the top 1-1/2" supply tapping C. This creates an air scoop at the hottest point in the system. this is where all the micro-bubbles will gather and find their way to the expansion tank...
Unfortunately, the theory that the 1/2" port will collect all the air and send it to the tank isn't working out in practice. I can think of two possible reasons:
1. The 1/2" copper pipe to the tank isn't pitched correctly. It's perfectly level, with one short vertical, unlike the Airtrol installation instructions that say to pitch the pipe a minimum of 1" per 5' of run. We definitely do not have that pitch.
2. The Airtrol instructions say to use a minimum of 3/4" pipe for that pitched run to the tank. We have only 1/2" pipe. I realize the boiler port itself is only 1/2", but I'm wondering if transitioning to 3/4" copper pipe above the valve shown below, and running correctly pitched 3/4" pipe all the way to a new Airtrol fitting on the tank would help. The Airtrol specs say the fitting itself has a 3/4" female pipe thread, so 3/4" threaded adapter would thread directly in. (The pic below shows our current setup with 1/2" iron pipe from the boiler to the ball valve, and then 1/2" copper above it.)
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