How to bleed air out of a heating system (C) Daniel FriedmanHot Water Radiator Air Bleed Vent Diagnostic Guide
Troubleshoot Hot Water Heating System Air Vents

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Air bleeder valves & automatic air purging valve troubleshooting & repair for hot water heating systems:

FAQs: here we focus on how to find, install, diagnose & fix these devices.

Here we explain how to diagnose and repair problems with air bleed valves and we describe methods used to remove un-wanted, air from noisy or air-bound hot water heating system pipes, radiators, convectors, and baseboards. We illustrate how to buy and add air bleeders at baseboard elbows using a baseboard tee and air bleeder valves.

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Hot Water Heating System Air Bleeder & Vent Troubleshooting FAQs

Radiator valve with air bleeder (C) Daniel Friedman

These questions & answers about heating system air bleeder valve installation, troubleshooting & repair were posted originally at AIR BLEEDER VALVES

On 2017-07-31 by (mod) - how difficult is it to remove & replace a rusted old air bleeder valve on a cast iron radiator


It's a perfectly fair question: but one that involves a bit of arm-waving to answer. Normally it's trivial to un-screw a small-tapped or threaded plumbing part. The arm-waving is that if there have been leaks or the connection is quite old it may be rusty as heck.

In that case I would NOT try this repair during the heating season when we might be left having to leave the heat off because we tried to remove the bleeder, broke it off and now have a radiator with a hole in it.

First: it may be possible to replace just the bleeder core. See our AIR BLEEDER VALVE REPAIR article.

Else you'll have to remove and replace the bleeder. First buy a new one of the same sized tapping.

Then ...

Off season, heat off, system cooled down, no pressure, try squirting a bit of Liquid Wrench on the threads, then try un-screwing the valve using a suitably-sized wrench that turns the valve from its base.

To install a new valve you may need to clean up threads and use teflon tape or paste.

Use the page top or bottom CONTACT link if you want to send me photos of the situation and perhaps we can comment further.

On 2017-07-31 by Fred

How hard is it to remove an air bleeder valve (1/8 inch) on a hot water system installed in 1980. The house is 96 years old and was heated by oil with the change coming in 1979 but the first heating season in 1980. It's a manual valve which used a skate key to bleed but the stem seems t have broken off. There is no leakage of water just concerned about being able to remove the old valve and not cracking the valve with the threaded portion left inside the radiator. The radiator is made of solid cast iron.

On 2017-03-15 15:31:53.959804 by (mod)


If there's no air released at an air bleeder valve , and if water comes out of the valve when you open it, then either the system is not air-bound ,or it's air-bound in a section or piping not serviced by the bleeder valve.

If the heating pipes don't get hot I'd start by seeing if the boiler is running in response to a call for heat (or at least check temperatures at the boiler) and I'd see if the circulator is working or zone valve is opening.

On 2017-03-15 03:29:55.862909 by Allen

I guess I was wrong. After checking back to the pipes on either side of the valve, although now just room temperature, the piping remains the same temp. I tried the lever 2 more times, waited, but no more gurgling or air sounds. What do I do now?

On 2017-03-15 03:20:29.270243 by Allen

The bleeder valve is a finned unit in the center of two water valves about 12" apart. A flat stamped metal lever moves from the normally up position to a fully down position.

An opening in the front of the baseboard unit allows an easy release and upward push up of the lever. I've moved the lever twice and heard air release and then water gurgling. The piping on either side of the bleeder valve is now warm. Have I successfully bled the system?

On 2017-02-07 14:19:58.553111 by Maurice

I've encountered a corroded bleeder valve on a base board heating system. I want to replace the bleeder valve. Is this a relatively simple DIY project for someone mechanically inclined?
Can you give simple step by step instructions?

On 2017-02-05 20:21:34.245755 by Pamela Miller

I think I have air bound in the system but when I look at the valve,instead of a slot,it's rounded like a cap. Is there a way to bleed these valves?

On 2017-02-03 12:41:46.634724 by Joe

Hot water heating system. Does not heat properly. Radiators get warm but not as hot as they should get.

Have had a number of boiler people in. They say the boiler and thermostat are fine . I have to bleed air from the first radiator regularly. So I am now pretty sure that air is being trapped on this one zone (I have 4 zones) between the boiler and the first radiator in line (it is a long line to the first radiator).

When I look at the line coming out of the furnace I do not see any air release valve above the boiler.
Two questions.

1. Should there be an air release valve on the zone line coming out of the boiler in the basement?

2. Instead of a manual release valve on the first radiator should I have someone install an automatic one?

On 2017-01-08 21:50:08.535829 by (mod)


I can't guess from your question if the problem is an airbound heating system or a problem right at the boiler, or a bad circulator pump, or something else.

But certainly repeatedly bleeding water doesn't fix anything. If no AIR can be bled from your baseboards or radiators, then you can stop the bleeding procedure.

The system could still be air-bound if air is blocking a pipe that doesn't happen to slope or rise such that its air moves to the point where you're doing the bleeding.

BUt before fooling more with air bleeding I'd call for help from your heating service company. Or to read more yourself search InspectApedia for COLD RADIATOR DIAGNOSIS & REPAIR to see other causes of these problems.

Keep me posted.

On 2017-01-08 01:15:41.057044 by bobby

if any one can help me email is need help getting the heat to warm up the house baseboard heaters just barly get warm and stop after letting water and air out pls help

On 2017-01-08 01:07:44.569267 by booby

what should i do i bleed my baseboard heaters let air and water out multiple times and only a lil heat comes out of them then they stop i really need help dont know nothing about boiler heaters and its cold in south dakota pls help

On 2016-12-19 16:45:21.974788 by (mod)


Hearing gurgling water means you didn't get all of the air out of the system. If you install an automatic float type vent at the high point of each baseboard run that might work for you. (Check periodically for water leaks).

On 2016-12-19 16:44:25.792556 by (mod)


Look at the start and end of each hot water pipign run as well as at the start or end of baseboards or radiators; for older cast iron radiators look at the end-top of the radiators

On 2016-12-19 15:36:10.475542 by roger

have cast iron baseboards. 2 story home. I bleed off the air on the upper floor radiaters during the winter but at night it sounds like water is running when the heat is on. Any help with this?

On 2016-12-18 19:43:00.455299 by Sharif

Where can I find the air vent in my floor heating system in my flat? I think it is not working properly, the heating is distributed unevenly through the floor and I suspect that because of the air in the system.

On 2016-12-11 03:25:05.653623 by (mod)


You might want to search for


There are a number of possible explanations for the problem that you described. I would start by saying that they heater is running in response to the call for heat at the thermostat if it's not it would make sense to call your heating service person for repair.

On 2016-12-10 23:57:22.401328 by Karen Kelly

Baseboard registers are warm (barely) to the touch. Thermostat set at 82° but only reads 71°. Daughter bleed the individual registers, but they are still barely warm. Just bought this house in June and have no idea what to do next.

On 2016-11-30 15:11:10.999665 by Ken Gorman

Hi there I am experiencing problems with heating hot water mainly no good flow through the coil, I have tried all the normal venting etc and all valves are operating. The main problem is if i turn pump speed up from 1, to 2 or 3 to try and get full flow, the expansion pipe in the F & E starts sucking air in ?
Want do you think I should try next Ken

On 2016-11-29 19:05:18.857339 by Will

Well, I left it a few days and still no air in either zone. One other thing I did was manually operate the fill valve while the system was running, the pressure is up to 30-35 psi now. Not enough to trip the relief valve and it seems to be working.
Either that....or I finally got all the air out.

On 2016-11-23 03:09:23.091718 by (mod)

AUTHOR:Will (no email)
COMMENT:No bleeder valves on my radiators but the 2nd floor bleeder valve was closed, that was the zone that had a lot of air in it last night, after I bled the first floor. (I forgot to check the second)
When I opened the second floor valve and pushed the pin I got water.

When I turned the heat on I got heat and no where did all that air go ?

Has the bleeder valve worked whilst I was upstairs waiting for the heat to work it's way upstairs ?

I guess I'll leave it a couple of weeks to see what happens. Thanks for your help and suggestions !

On 2016-11-23 02:34:35.398611 by (mod)

If I assumed you meant bleeder valves, not blender,

Then I'm guessing but if one opens the air bleeder valve on an upper floor when the heating system is not up to full operating pressure indeed air may enter rather than exit.

You need to be sure that the heating system is up to full operating pressure before trying to bleed air.

On 2016-11-23 01:31:54.774427 by tim

My second floor zone 1 has two blender where the pipe comes up, and one where it goes down. When I open either, it sucks air into the system. The pipes are loud and gurgling. Any ideas?

On 2016-11-22 23:10:17.954120 by (mod)


AS SOON AS YOU SEE WATER coming out of the air bleeder valve, close it - you're finished there. DO NOT bleed any extra volume of water out of the system; that won't help anything and it just requires more makeup water at the boiler.

On 2016-11-22 23:09:26.276210 by (mod)


Very good question. Something's wrong for sure. Either you're not getting all of the air out of the system, or there is an air leak into it.

I'm doubtful about air leaks into hot water heating systems as the system is usually under pressure, but it's possible that during cool-down an opening, such as at as bad circulator mounting pump flange might leak air in as well as other times leaking water out. Look for signs of water leaks around the boiler.

An over-charged bladderless expansion tank might also inject extra air into the heating system. BUt that would find its way out through float type bleeder valves or manual air bleeding.

Most likely: you've got a larger air reserve elsewhere in your heating system - such as at a long horizontal nearly dead-level piping run, and it's taking some time for the circulator to push air through the system to the point where you're trying to bleed it out.

Try the AIR BLEEDER DIAGNOSIS article recommended at CONTINUED READING at the end of this article or at AIR BLEEDER VALVES

On 2016-11-22 19:48:17.396120 by Louise

How much water do I let out before I close the valve?

On 2016-11-22 10:08:34.397359 by Anonymous

As I bleed the system it keeps on refills with air?

On 2016-11-22 00:25:54.594974 by Will

No bleeder valves on my radiators but the 2nd floor bleeder valve was closed, that was the zone that had a lot of air in it last night, after I bled the first floor. (I forgot to check the second)

When I opened the second floor valve and pushed the pin I got water. When I turned the heat on I got heat and no where did all that air go ? Has the bleeder valve worked whilst I was upstairs waiting for the heat to work it's way upstairs ?
I guess I'll leave it a couple of weeks to see what happens.
Thanks for your help and suggestions !

On 2016-11-21 23:02:58.354730 by (mod)


Air in a float valve pushes an internal float that in turn opens the valve from the inside.

Your radiators may also have air bleeder valves.

On 2016-11-21 21:57:08.664374 by Will

Thanks for the info

1) OK, the caps are loose

2) I didn't know there was a pin in the valve, I'll check that tonight. However, if I have to push the pin to let the air out how is it let out automatically ?

3) I'm probably going to do this anyway

4) I don't think I can have both since each radiator is fed through the floor (hardwood) and the returns go back under the floor and on to the next radiator.

There are no sections of pipe visible worth mentioning. I will think about adding bleeders in the return side above the furnace though.

My guess is that the bleeders I have are stuck and that the air isn't being vented - where is the air coming from, city water presumably. I have no visible leaks that allow air in (and water out) although in reality it could probably quite easily be leaking unnoticed.

I'll swap the valves and see what happens.

Thanks !

On 2016-11-21 21:14:41.691727 by (mod)


I'm not sure what's going on at your system, but

1. the screw cap on float type air bleeder valves is normally left loose all the time so that the valve can automagically vent air when it grabs some.

2. If you remove the screw cap and press down the schrader valve pin in the air valve and water squirts out, then there's no air at that point to be vented

3. If the air valves are really stuck and not venting air - say from build-up of corrosion, yes certainly I'd replace them.

4. GOod last question. Yeah there are actually air purgers at several high points in a system.

Air can get trapped such that it is grabbed at *local* high points such as right over the boiler.

For example air might be pushed or pulled through a zone pipe into the boiler on the return side, then it bubbles up the boiler output riser and hopefully is vented there.

So you want both: air vents at the boiler on the outlet side and on some systems on the return side too - as well as at other high points in the piping system.

On 2016-11-21 14:42:13.139837 by Will

I keep getting air in my system and have to purge it every couple of weeks. I opened my automatic bleeders and nothing comes out, should I screw the caps down tight after purging the air using the shutoff valve and drain spigot method ?
Since nothing comes out of the bleeders should I replace them ?

Also, my furnace is in my basement, the bleeders are on elbows maybe 3-4 feet above the furnace but probably 2 feet below the run of radiators so obviously not the "highest point". Does this matter ?

On 2016-11-13 18:34:59.664903 by Michael

Thank you! this article is very helpful. We love our hydronic heat and I want to make sure I keep it running well, this was just what I needed, thanks.

On 2016-10-19 18:23:43.244484 by (mod)

Harry, the little key tool you described is widely sold in several sizes of which 1/8" square is standard; it's described as a Radiator Air Vent Key or Radiator Air Bleeder Key, for less than $1.00 each. You'll find these at your local hardware store if your are lucky enough to have one that's not been squashed by the big box stores.

On 2016-10-19 17:31:51.579072 by Harry Rust

I want to bleed the air "if there is any trapped" in all the old heavy radiators in my house. I don't know the proper name of the tool used to do this but I think it looks similar to a key. Anyway, I need to know where to get one. Thank you.

On 2016-10-13 16:37:17.245268 by James M

i have a unique outdoor wood boiler system with one forced air coil and a side arm heat exchanger. I am a plumber by trade but amd having trouble with this particular scenario.

The wood boiler im using has an atmospheric port at the boiler outside, which is about 10-15 feet below the highest point in my heating system. with great difficulty i am able to get all pumps primed but once running the air is still present in the pipes. and after a day or so i get air lock from air bubbles pooling in high spots.

I cannot use auto air vents because of the open port at the boiler as soon as i open a valve to bleed air it sucks more air into the system due to the negative pressure that the system is running on... im about to get a airscoop but will it work under this negative pressure scenario? thanks for any feedback. (p.s. winter is upon us)

On 2016-10-10 13:36:59.345177 by (mod)

Only air should come out of an automatic air bleeder valve; If the valve begins leaking water on its own, that is when you're not fooling with it, it needs to be replaced.

If water comes out of an air vent that has been manually opened then it should be closed, and we can infer that there is no air present in that part of the heating system piping.

On 2016-10-09 20:49:06.304076 by Anonymous

Only Air comes out but no water or very slight?

On 2016-01-29 22:12:52.686047 by ryan

I opened the value on my forced hot water baseboard and air came out then a minute of water and air came out. It went on for more then a minute is this normal? And does the water automatically refill?

On 2016-01-29 22:09:40.307808 by Anonymous

air came out with water for more then 1 minute?

On 2015-11-23 13:35:13.613216 by (mod)

Bob search for AIR BOUND HEATING SYSTEM = the zone that is not heating may be air bound; or if you have separate circulators, zone valves, or thermostats, one of those controls for the cold zone may need repair.

On 2015-11-22 02:58:44.652434 by Bob

One of the pipes that circulates water in the heating system is not hot. Others are hot and heat is fine for those rooms.

On 2015-10-20 03:35:10.436452 by Anonymous

Automatic bleed valves are normally left open.

On 2015-10-20 02:09:02.459099 by Bill

I have a bleeder valve on the top of a pipe between the joists in the ceiling of the basement (above the oil fired furnace/hot water heater). It is cracked open, like a permanent vent/bleed. Is this correct? Seems to me that they should remain closed.

How do I Know if the Air Eliminator or Air Purger is Working on my Heating System?

As we explain beginning at AIR BLEEDER VALVES , virtually every hot water heating system has one or more air bleed valves installed. On most hot water heating systems there is at least one automatic air bleed valve, usually located on the heating boiler itself, or close to the heating boiler on a nearby check valve or flow controller.

If the automatic air bleed valves are installed in the proper locations on the heating system, typically at high points such as at or near the heating boiler and at one or more high points in the radiator or baseboard piping system, then small amounts of air in the heating piping will be purged automatically.

First, is there evidence that the heating system is not working due to air trapped in the hot water heat piping, baseboards, or radiators?

Check hot water baseboards, radiators, or heating convectors: if some of these heating devices are hot and others cold, are they all on the same heating zone? Feel the hot water piping leaving the heating boiler - it should be hot when the boiler is running and the thermostat is calling for heat.

If the building has multiple heating zones each zone will be controlled by its own thermostat and each heating zone will either have its own hot water circulator pump (controlled by a thermostat and pump relay switch), or each hot water heating zone will have its own thermostat and a zone valve that opens to let a common circulator pump send hot water through that individual heating zone.

Are all of the thermostats turned up high enough to call for heat in each heating zone?

If some heating baseboards or radiators are hot and others cold and we're sure that they're on the same heating zone, then the system is probably air-blocked.

Second: even if heat is working throughout the building and the heating system is not air-bound, there may still be air purge or air bleed valve repairs needed. Sounds of air gurgling in the heating piping is a sign that trouble is brewing, and leaks anywhere in the syste are also leading to trouble.

But a variety of problems can cause the automatic air purging valves to fail to do their job. The effort to fix these problems ranges from trivial to a bit of work. Failure to fix the air purge system can ultimately lead to loss of heat in all or parts of a building.

Question: bled air but still get gurgling sounds - where will I find secondary air bleeders

I have an under 10 year old baseboard hot water radiator system. I bled the main tank at the furnace but am still getting gurgling and water flowing sounds in some of the radiators. I assume there are secondary bleeder valves. Where are the likely places these might be located. Thanks - Jim 1/30/12


AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE has more thorough and aggressive means to get unwanted air out of a hot water heating system.

Question: I don't think my hot water heating piping air-bleeder vents are working

I have this type of radiator For someone reason the one closest to the boiler needs to be bled every day. I do not see any leaks. All other radiators function fine. It is a one floor house with one zone. Any thoughts? - Chris 1/3/13

I have three automatic air vents - one Spirovent and two Hy-Vents for three paralleled heating needs off oil-fired boiler. Former is on main whole-house distribution loop for Infloor radiant heating and one of latter is for DHW storage tank distribution loop. The last is on the far-side distribution loop of heat exchanger for sunporch with Infloor radiant heating. This loop has 50:50 mix with antifreeze because the temperature control is set for 50 degrees in Gypcrete slab temp and not air temp in glass/extruded aluminum sunporch.

This automatic air vent seems not to be working automatically anymore because this heating season I'm hearing entrained air 'tinkling' and 'squirting' through the circulator pump.

Even with pressure checked at 20 PSI.

This vent sits atop Taco air scoop with expansion tank under scoop and these three are downstream of pump which is piped in very soon after boiler outflow manifold.

I have checked that screw cap cover is backed off and have now depressed Schrader valve to release a 'highly carbonated' bubbly froth three times today and still haven't gotten all air out.

Other Hy-Vent on piping to DHW tank delivers only water when I depress Schrader valve. Can I clean this [faulty] unit without depressuring that loop? If so, how do I take it apart. Taco manuals I've found show nothing. Just replace it? Is the antifreeze to blame? Specifications said I could use it. Suggestions welcome. - Christopher D'Amico 1/14/2013


Christopher I think you might first take a look at our air bleed valve diagnostics beginning
at AIR BLEEDER VALVE DIAGNOSTIC FAQs to be sure we're on the same page.

As you are continuing to have trouble you will want to
see AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE where we describe methods to be sure you've gotten all the excess air out of all of the system components and piping.

Question: cold wall panel

Wall panel hot at top but cold at bottom. Cause and remedy please - John 7/29/12


John, so little information, sorry, no idea. I don't even know what kind of heat you are discussing.

Take a look at how the equipment is piped; if hot water is entering but not exiting a hot water radiating device it m ay be air-bound, or an exit pipe, valve, or trap may be clogged with rust or debris. For steam radiators that don't get hot the diagnostic procedure is different, as we may need to check the steam vents.

Air Bleed Valve Installation: How & Where to Install Manual Air Bleeder Valves on Hot Water Heating Systems

This topic has moved to a separate article: AIR BLEED VALVE INSTALLATION

Watch out: if the air vent or air bleeder valve is not installed properly, in the proper position (upright or horizontal depending on valve type and model), and in a functional location (where air can enter the valve or vent) it will not work reliably, may not work at all, and worse, may actually allow air into the water piping system, making the system air-bound frequency worse rather than better. Details are in the air bleed valve installation article cited just above.

Air Bleed Valve Leak Repair: How to Inspect and fix or replace leaky float-type automatic air bleeder valves (air vents):

This topic has moved to a separate article: AIR BLEED VALVE LEAK REPAIR

Air Bleed & Air Purge Valves for Hydronic Heating - Where to Buy Them

Question: Where can I buy canister type air bleeder or air purge valves?

We are unable to find the air bleed valves that you have listed on your web page (canister type). We are looking to buy 10 of them and am wondering if you have a contract from which to purchase these? W.M. - Wacol, Australia

Reply: W.M. please see AIR BLEED VALVE SOURCES where we list air purgers, air bleeders, manufacturers and sources. For a description of the different types of air bleeders or air eliminating valves you can also see AIR BLEEDER TYPES & LOCATIONS

What's the difference between an air bleeder valve and a radiator on-off valve?

Reader question: how do I differentiate between the valve to bleed the baseboard radiator of air, and the on/off valve? I just bought my house and I notice that there are 3 baseboard radiators in one section of the house that are cold. I think that perhaps they are turned off, but I don't know how to tell. Looking at the radiators, they have pull chains coming out of the top louver, but there's no tension on the chain like there is when you use a pull chain to turn on and off a light, so maybe the pull chains are for opening and closing the louvers?

When I take off the lower cover, the part that covers the fins, I see a valve on the pipe where the water comes in (or out?) that has a slot for a flat-head screw. Would I use that to turn on or off the radiator, or is that the bleed valve? I think it must be the former because I don't see where air or water would escape.

My heat is provided by a gas boiler forcing hot water to baseboard radiators, and I have only one thermostat. And another pertinent detail: In the basement the pipes going to those 3 radiators feel hot, so water is circulating.

In trouble shooting, I want to try the easiest thing first: are the radiators on? Then I'll move on to the more complicated procedures if that's not the problem. But how do I tell if they are on?
Thanks! - Anastasia

Reply: How to tell an air bleed valve from a radiator control valve ?

Radiator manual air bleeder valve (C) D Friedman

At left we show a manual hot water heating radiator air bleeder valve that has a round black handle. Because of the handle shape some folks may be confused about just whether this valve is an air bleeder control or a radiator on-off valve.

But it's easy to see the difference. The valve shown at left is attached directly to the hot water heating radiator at its top at one end. It is not connected to hot water piping, so it cannot be controlling the flow of hot water into or out of the radiator.

Now for more details:

At below left we show a common radiator control valve found at the top of a hot water radiator. Other radiator control (on-off) valves may be located close to the floor at the bottom of both steam and hot water radiators.

At below right our sketch (courtesy Carson Dunlop Associates) illustrates an air bleed found at the top of some older radiators - a model that has a tiny round handle. The advice in the sketch to leave air bleed valves alone is for home inspectors.

Radiator valve with air bleeder (C) Daniel Friedman

The worry is that opening an air bleed valve could lead to a leak if the valve is damaged or defective. But in fact manual air bleed valves on heating radiators are a control intended for use by a homeowner, need to be functional to get an airbound radiator back into operation, and need to be fixed if they're defective.

Radiator air bleed valve (C) Carson Dunlop Associates

The reason a home inspector might not operate the valve is that during a home inspection s/he doesn't want to risk starting a leak that can't be promptly shut off.

Other air bleeder valves have a t-handle or a square fitting operated with a "skate key" wrench and still other air bleeders use a flat bladed screwdriver for their operation - illustrated in the article AIR BLEEDER VALVES. In the sketch at above right you can see the radiator on-off control valve at the lower right.

Notice that the radiator control valve will always be connected to both the radiator and a hot water (or steam) pipe, while an air bleeder valve will be connected directly to the radiator.

Well almost. Our photo at above left is tricky because that particular model of radiator control valve also happens to include a little bleeder fitting - that hexagonal brass nut shown at the center of the radiator control valve body.

Question: difference between air vents and vacuum vents

(Dec 4, 2011) DanH said: Is there a difference between an air relief valve and a vacuum relief valve?


Indeed because people discussing plumbing parts may not always be precise nor use exactly the "official" name for a part, the two valve names you cite might be used by some to refer to the same device. But to me, if we are discussing well and water supply systems, then these are different devices.

An air relief valve would allow excess air out of a pressurized system.
A vacuum relief valve would relieve vacuum - the opposite of air pressure.

Can you tell me what kind of equipment on which the valves you name are used? If so I can write a more accurate reply.

Question: attic air bleeder vent not working

(Feb 15, 2014) Anonymous said:

We have hot water boiler system and there is air in the lines. The bleeder vent is in the attic and I am not sure how to bleed it. I has a stem that comes out of the top of the bleeder.



The air bleeder in the attic should be removing air automatically; If it is corroded or leaky it needs replacement; If it looks clean, try pressing gently on the center pin or valve stem (you may have to unscrew a cap that looks like an automotive tire air valve cap).

Just press the exposed pin briefly with a pen tip or similar instrument. If AIR comes out then the bleeder was not working automatically.

If water comes out STOP PRESSING as you're making a mess and no air is coming out at this location anyway.

If you mess with the valve stem pin as I described and now the darn thing won't stop leaking, just screw the valve cap back on as a temporary fix until the valve can be replaced.

If no air, just water comes out of this valve but your system is air bound, there may be other air bleed valves, automatic or manual, that need to be checked, tested, or replaced; on occasion we have to add a bleeder at a problem spot, and in the worst case we use other methods (described in this article series) to force air out of the system.

Watch out: My consultant Paul Galow suggested I add this warning: in the event of having created a catastrophic leak you'll end up having to turn off heat and turn off water supply to the boiler - an event that seems to me unlikely as long as you keep that valve stem cap to close off the valve if it's leaking or dripping.

But DO NOT use great force turning anything - some of these air bleeder valves are made of thin-walled copper. You can break one right off if you're heavy handed.

Question: drumbeats from the hot water radiators

(Oct 28, 2014) Anonymous said:

After what sounded like Congo drum playing occurring in my hot water radiators, I tried to investigate.

ll but one radiator was heating up. I have been bleeding the radiators - hear the hissing air until it finally stops, but no water coming out. I've bled them years past where water would escape.

Not sure what is going on. The one radiator that wouldn't heat up now is. Do I need to keep bleeding the radiators until water comes out? Thanks.


See BANGING HEATING PIPES RADIATORS - for diagnosis and repair of this problem

Question: how long do I keep the air bleeder valve open on a radiator?

(Nov 13, 2014) Anonymous said:

do I need to keep bleeding the radiators until water comes out


es but ... If you find that bleeding air put of a radiator gfets it heating normally but that after less than a whole heating season the air problem returns, then further investigation for a source of air leaks in or water leaks out is warranted.

Question: heating system shuts off with a loud bang and rattle

(Nov 19, 2014) Shelley said:

Our system shuts off with a log bang and rattle. Right at shut off is the only time we get air to purge from the pipes but it seems the more we do it the louder it is getting to where I worry we will have a joint blow apart



Watch out: I'm not sure from just your note what is going on - but it COULD be a *dangerous* puffback or fuel problem. I'd ask for an inspection and service by a trained heating service tech.


Question: opened bleeder valve, no air came out

(Nov 19, 2014) marc said:

I turned the little skate key device I have to Open the air bleed valve and there was no hiss air or water coming out it mentions that the valve body is clogged or blocked is there any way to easily fix this problem or is it a complicated fix? thx



The heating system needs to be on and up to operating temperature - check that and try again.

Details of what to do for this situation are at AIR BLEEDER VALVES

Reader comment:

Anonymous said:

11/27/2014 Anonymous said:

Couple of things-[about what to do if no air comes out of an air bleeder valve] -If your system is not filled with water, you can't bleed the air out of the topmost radiators.

You may need to open the fill valve in the basement, then bleed until air comes out.

Typically, the pressure limiter valve in the basement will drip a little bit after the system is full of water, but usually this stops after a day or so.

Also--if your system has the "scoop" type of automatic air purger, it can still get air bound in the top story of the house. Then you simply have to open the valves in the system in the basement until all the air is out. Takes a while to figure this out.



Good point and thanks for the comment - indeed in More Reading links at the end of this article you'll find two articles



that describe how to get past an air-bound system when the bleeder valve alone won't do the trick.

This article series provides a detailed guide to using air bleed valves to get rid of unwanted air in hot water heating systems: fix cold or noisy hot water heating radiators or baseboards. Hydronic heating air vents and air purge devices: types, where to buy; How to diagnose and fix heating system noises & air in hot water heating system pipes.

Service Procedures to force air out of an air-bound hot water heating system.

How to bleed a hydronic (hot water) heating system: how to purge air out of heating system boilers, radiators, baseboards, or piping. What is a baseboard tee, how do they work with baseboard air bleeder valves, how to install air bleeders, vents, purgers.

Question: reasons to add air bleeder valves at the end of zones

(Dec 3, 2014) LarryM said:
I've got a 3-zone baseboard heating system that keeps getting airbound.

There's an automatic bleeder by the boiler, but no sign of any bleeders anywhere else.

I'd like to add bleeders at the topmost point of each zone, but the pipe comes up from the floor into an elbow, then immediately into the radiator, then there's another elbow and the pipe goes back through the floor. It seems to me that there's no slack to be able to unsolder the elbow in order to replace it with a baseboard tee.

What are your thoughts on adding the automatic bleeders to each zone in the basement, where I have free access to the pipes? Also, what are your thoughts on using a saddle tee to add a bleeder?

(The circulator pumps are on the far end of each zone, if it makes a difference.)



Sometimes the problem is that we didn't successfully purge all of the air out of the system in the first place. Sometimes it's hard to get all the air out of long horizontal piping runs.

A second possibility is that there is a leak somewhere.

Sure you can add air bleeders at the ends of high end of each zone.

Question: persistent cold radiator

(Feb 21, 2015) joe s said:
One radiator keeps getting cold even after bleeding. When bled water came out but air bubbles still present. Do I keep bleeding till no bubbles? Thanks


Joe, if you're getting mostly water out at the bleed valve I suspect the problem is ahead of the radiator, at it's control valve or air in the heating lines ahead of the radiator. You may need tonuse one of the procedures discussed at AIRBOUND HEATING SYSTEMS in Continue Reading At area at the end of this article.


(Feb 18, 2015) Anonymous said:
Here is my situation. I own a 3 story commercial building. It is a boiler heat system. This system was probably installed somewhere in the 1930's or earlier, if that's possible. Anyway,on the third floor, the radiators that are first in line receive hot water. The last three or four do not. I have opened all air bleeders on the the radiators on the third floor at the same time.

The first eight radiators all bleed fine.The last three or four do not. Sometimes on these last four, two of them will bleed water and air and the last two do nothing.

These last radiators are in the area that we use as our offices and we need heat. I understand that there is air lock here somewhere. The problem is that I can't get all the air bled out from these radiators and they remain cold. I've read your articles here and they provide great information. Thank you.Any ideas as to how or what I can do to get these radiators up and operating?
Wayne in Latrobe, Pa.



For bleeders that do nothing they're probably clogged and should be replaced.

Check that the radiator valves actually work rather than just the handles spinning. Check for air bound piping ahead of the cold rads or clogged radiator return piping.


(Feb 17, 2015) SteveF said:
A few years ago we had a section of our hot water heat removed because we were planning to remove a wall between the kitchen and living room. To make up for the lost heating or those radiators, they put PEX under the floor in the entry way and kitchen only. But ever since then I can't bleed the system out like I used to. It actually sucks air into the bleeders.

So I've left it alone but I still hear gurgling in the pipes and radiators although it seems to heat fine. But I know it's not as efficient and probably not good for the system. Why would it suck air in? I can take water on my fingers and turn the bleeder and see it get sucked in. Thanks a bunch.



From your description it sounds as if those air sucking bleeders are not in the right location -leave them closed. Try bleeding from higher bleeders,
Or install a higher located bleeder, or use one of the other methods we discuss for forcing the air out of an AIRBOUND system using a pony pump.

Question: not enough heat from radiator

(Feb 21, 2015) lester said:
I would like to know what can cause my radiator to give out little heat. I checked the pipes and they are hot


In the More Reading links just above please take a look at one of the COLD RADIATOR ... Articles for some diagnostic suggestions


(Mar 1, 2015) david said:
I have been trying to purge my 2 heat pump zone system with little luck getting all the air out. I have put city water pressure into the boiler @ the boiler drain,

forcing the water through each zone pump individually and together with the loop closed and the bleed drain open, all with the gas valve off. ran until no air bubbles were present. Then I started the boiler up (turned on the gas valve and called for heat) There is still a lot of air in the system. Can a boiler make its own air when cold water is introduced to the hot system by the fill valve when bleeding?



There could be a water leak out and air leak into the system, or it could be that you need to use a more powerful air purge approach to force air out of horizontal piping runs.



in the More REading links above

(Mar 3, 2015) David said:
Thanks for responding Dan. I've checked for leaks and I never hear the fill valve open. I've used city water pressure at the drain valve as i've said, and there is little or no air. I've checked the city water for air(none). It seems to me there is only 2 possibilities:

The fill valve is sucking air when i'm bleeding, or as you stated, I'm just not getting enough pressure to force the air out. I also tried using a "L" shaped 1/8" fitting @ the highest point of the upstairs zone with a hose attached and opening an 1/8" valve there and open it when the air comes by. This seems to work as a lot of air comes out.

But it seems to make the air worse, hence my ? about cold water causing air to be released when bleeding. If I shut the gas valve off and try the above method, air comes out for a while then stops. Turn the gas back on, then more air appears.

How can I check my fill valve for "air sucking" and how can I do a more powerful air purge?


When the heating system is cooling you can feel with a wet finger whether or not there is suction at the air vent opening.

Question: American Air Purger as illustrated in this article, which is automatic? I have excessive gurgling, bubbling, and banging

(Feb 2, 2015) GorRiv said:

I have an American Air Purger as illustrated in this article, which is automatic? I have excessive gurgling, bubbling, and banging in my baseboard system though.

Can/should I crack the valve at the top to bleed off air? Should I make sure the water intake for the boiler is open, and how much/when? Everytime I try to access other pages about Air bleeding they come up with "error, problem loading page". Help, please.


GorRiv -

Check that the valve cap is loose and that the valve is not leaky or clogged with mineral salts from prior leaks - or just replace it.



Continue reading at AIR BLEEDER VALVE FUNCTIONS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AIR BLEEDER VALVES for an explanation of how these valves work and how to use them.

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AIR BLEEDER VALVE DIAGNOSTIC FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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