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Leaky hot water heating system vent repairs - how to repair a leaky hot water air vent or bleeder valve: here we explain how to repair or replace both manual heating system air bleed valves and automatic float type air vents that are leaky. Float type automatic vents on hot water heating systems are normally left "open" to automatically purge air from the system.
But a float vent that leaks water will stop working, may leak onto and damage equipment, and is often left "closed" or shut off as a temporary measure. And a manual air vent that is leaky or that no longer vents due to corrosion and clogging is not going to do the job when your heating system is airbound and radiators or baseboards are cold.
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Air Bleed Valve Leak Repair: How to Inspect and fix or replace leaky float-type automatic or manual air bleeder valves (air vents):
Is there a little cap on top of the air bleeder? many air bleeders use an internal float and an air valve stem that is about the same as the valve stem of an automobile tire valve or bicycle tire valve. The cap over these valves looks just like the cap on the valve stem on a tire (it is).
But on an air bleeder the valve cap is normally left loose so that when the valve has accumulated enough air to move the internal float the valve can open to expel the air.
If the valve cover is screwed down tightly, or if the valve cover has become clogged with mineral debris left by leaking water, air cannot be released. Loosen the valve cap.
If air escapes when you loosen the valve cap on the air bleed valve, that's good.
If the valve cap on your air bleeder is badly corroded (photo above left) the valve probably needs to be replaced.
If the automatic air purge valve has become corroded and/or leaky: the air bleeder valve is of the automatic float and canister type rather than manual type; among these. Automatic air bleeders, to work, require that their little screw cap (it looks like and is a tire valve stem cap) be left loose so that the float inside the automatic air purger/bleeder can release air when needed.
Usually automatic float type air bleeder valves are installed at the boiler where it's easy to see and replace leaky ones during boiler service. I don't recommend using float type automatic air bleeders at heating baseboards inside the building where they may be hidden by baseboard covers and can leak into and damage the building for some time before anyone notices.
Additional automatic air bleeder valves may be installed at other points on the hot water piping, usually at a higher spot near the boiler and sometimes on upper floors in the building.
Look for and check the operation of these air bleeder valves too.
How to Protect the Building from Water Damage from a Leaky Air Purge Vent
If water starts to leak out of the air bleeder valve continuously (photo at left) (it's ok for a drop or so to be expelled if the leak stops quickly) then screw the cap down tight again and ask your heating service technician to replace the valve.
Taco® provides a neat little attachment, the Taco Hy-Vent waste connector (sketch at left, adapted from Taco's product literature), that connects to the company's Hy-Vent air purger. The Hy-Vent waste connector allows the Taco Hy-Vent's outlet to be connected to a suitable drain location so that should the valve begin to leak through its vent opening water will be directed to a drain without damaging the building.
Watch out: Taco warns that while connecting a 3/4" flexible hose to the air vent outlet can suit to protect building areas from water damage, do not solder a connection to the air vent valve. Soldering the air vent outlet will cause it to fail to operate properly.
[Click to enlarge any image]
In our OPINION it would be smart to also inspect for leaks at any and all piping connections, including the threaded air vent mounts, and it would be smart to direct a waste connector vent drain to a location where somebody will notice that the vent is leaking so that proper repairs can be made. See AIR BLEED VALVE SOURCES.
Watch out: reading the installation literature from a variety of air eliminator and air vent manufacturers we observe that instructions about how to leave the air vent valve cap vary. Generally the cap is left loose to permit automatic air purging from float type air vents and partly loose to permit automatic air venting from some models of coin vents. But some instructions such as for the Honeywell EA79 Air Vent want you to leave the vent cap shut, stating
How to Fix or Replace Corroded or Leaky Manual Air Bleeder Valves
Is the air bleeder valve corroded? If the air bleeder is thick with corrosion or mineral deposits (photo at left) it has probably been leaking water when it should not, and it probably needs replacement.
Inspect and use or replace manual air bleeder valves on the heat distribution piping:
Problem spot manual air bleed valves: If a building heating system has experienced previous problems with air blockage in the heating system a technician may have installed a manual bleed valve at a strategic location to get air out of a problem section of piping. Look for valves that resemble the one shown in our photo.
Problem finding all of the air bleeder valves: air bleed or air purge valves on hot water heating piping or baseboards can be hard to find. Usually, in addition to one or more automatic air purge valves found at or close to the heating boiler itself, you will find an automatic or manual air purger at the higher end of a section of heating baseboard that has become air-bound in the past.
Leaky air bleeder valves: I find leaky air bleeder manual air bleed valves as well as automatic or float type air vent valves on heating systems.
Sometimes the manual air vent is leaking just because the manual air bleed valve was left open or was abused by a heavy-handed operator who over-torqued its fittings and damaged screw threads or a seating gasket
Tips for Step by Step Replacement of a Damaged or Leaky Air Bleeder or Vent are at AIR BLEED VALVE INSTALLATION
Manual Air Bleed Valve Cleaning & Parts
At below left you can see a disassembled manual air bleed valve. The smaller threaded stopper component screws into the center of the air bleeder body until its tapered tip is snug against the valve seat. At below right you can see the tapered air bleed valve seat against which the rotating stopper meets.
Below you can see the vent opening in the side of this air bleed valve. When we unscrew the center stopper in this valve (turning the screw counter-clockwise or from right to left), we open the valve just enough that air can pass through the bleed valve body and out at this vent opening.
Watch out: You do not normally need to fully remove the bleed screw, and you shouldn't. If you remove the inner screw completely you'll have a hell of a time fumbling it back in place when hot water comes squirting in your face. Don't do it.
Just one full turn should be enough to permit air (if present) and ultimately hot water from the heating piping system (when there is no air present) to squirt out of the vent.
(On the air bleed valve shown here, about six full turns of its center screw will completely remove that component from the valve body.)
As soon as water begins to exit the vent body you should close the screw by turning it clockwise to a firm, closed position. Wipe off the vent body and check that it is not leaking. The vent shown and most of its sisters are made of stainless steel, are corrosion resistant (not corrosion proof), and should not easily clog with debris.
How to Clean Debris from a Clogged Air Bleeder Valve
If on turning the air bleed vent screw one full turn no air and no water vent out of the bleeder, either the baseboard, pipe, radiator, or convector being bled is completely empty of water and is under no pressure whatsoever (abnormal conditions) or the valve opening or its vent exit opening may be blocked with debris. Small bits of debris will normally vent successfully through the vent opening shown above when the valve is opened.
For an air bleeder that is covered with mineral deposits or lime from prior leaks, you could remove the valve, disassemble its parts, soak them in vinegar over night to loosen the lime, but frankly that's a risky approach. Given the trouble and disruption of removing an air bleed valve in the first place, and the risk that it will still leak on re-installation, just replace it instead.
Watch out: do not try to clean an air bleeder valve seat using abrasives. For successful closure, the air bleeder valve shown depends on a good fit between the tapered screw tip and the tapered valve seat in the valve body.If you scratch or scrape the valve seat or the mating face of the valve screw the valve may fail to seal completely. The air bleeder does not contain any plastic or rubber seals.
Reader Question: how do I solve problems with leaks at an air bleed valve and air remaining in the heating system?
I recently installed a new hot water furnace in my house. I did the job myself and everything is working ok except that the automatic vent valve constantly needs to be opened to let out air.
I left the cap loose so that it could vent automatically but then it leaked. Do you think that the valve is bad or is not placed in the proper location ? Any help would be appreciated. - E.M. 12/27/12
E.M. A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with air bleeding or air leaks into hot water heating systems. (Incidentally, for clarity we call hot water heating systems heating boilers or hydronic boilers - furnaces are generally warm air heating systems).
That said, if you are continually seeing air bleeding out of your air bleed valve then I suspect that either you have not fully bled all air out of the system or there is a leak somewhere that is both letting water out and air in to the heating boiler or its piping and radiators / baseboards. I suggest checking all of the heat piping, baseboards, radiators &c. to see if everything is getting hot.
if your system is successfully circulating hot water through all of the piping and heating devices but there is still air in the system (and if there are no leaks) then it should be pretty easy for the automatic air bleeders (properly located at high points on the boiler and on the heat distribution piping) to purge the remaining air.
Air Coming out of the Bleeder is OK, Water Coming out of an Automatic Air Vent Means Valve Replacement is Needed
Observing air coming out of an air bleeder is not an indication of a faulty air bleed valve. And if you are indeed seeing air venting out of the valve its location is a functional one. However that does not mean that it's the only air bleed valve needed.
What would be a fault would be water coming out of the air bleeder valve, such as I demonstrate in my photo at left.
[Click to enlarge any image]
Float type air bleed valves are supposed to stop venting once water enters the valve body.
I agree that if water is leaking out of the air bleed valve that's not an acceptable condition - the valve needs to be cleaned (try purging a little water through the valve to flush the valve seat) or replaced.
In an emergency I too would leave the air bleed valve cap shut tight to stop a leak but I wouldn't leave that as a long term solution, as leaving the cap tight also prevents the valve from bleeding excess air from the system. If you can't get the valve to stop leaking, try replacing the valve core stem or replace the entire valve.
Typically we see an air bleeder located close to (above) the boiler itself and one or more located at high points in the heat distribution piping. If you are having trouble bleeding air out of your system you might need to add another air bleeder at the high end of a heating distribution loop, or you might need to follow our suggestions for manually forcing excess air out of a system. AIRBOUND HEAT SYSTEM REPAIRS
Reader Question: Leaky air bleeder on a Slant-Fin "radiator"
We live in a 45-year old house with baseboard Slant-Fin radiators. One of the air bleeder valves has started to leak, It's a slow leak. but enough to do some real damage if we don't fix it. Upon inspection, we found that all the bleeder valves in the house are horribly corroded and would like to have them replaced. I don't want to attempt this myself (I'm somewhat handy, but the thought of screwing up and losing our heat in the middle of the winter is horrifying) So what kind of specialist should I call? - Dave Selander 3/4/12
A heating service technician or a plumber experienced with hot water heating piping can do the job you describe. It's least disruptive to schedule the repairs for out of the heating season.
When Should a Heating System Air Vent Valve Cap Be Left Open or "Loose"
Opening up a an automatic air purge valve whose cap was closed
If loosening the valve cap does not make water leak out, leave the cap loose. This permits float type air purge vents and some other automatic air vents to do their work. If the valve is leaking you will need to leave the cap closed tightly to avoid water leaks and damage, but you should then replace that float vent or auto-vent at next system service.
Shown at left, the air vent cap on a Maid-O-Mist No. 67 auto vent, automatic air eliminator. Notice the vent hole in the device cap? When this valve cap is left loose air can vent out of this opening.
[Click to enlarge any image]
Watch out: make a list of the locations of all of the air vents on your heating system and post it near the heating boiler. An occasional inspection of each vent for signs of leakage can stop trouble before it results in loss of heat or water damage to the building interior.
Watch out: for automatic and some manual air vents the operating water pressure in the heating (or cooling water) system must be higher than atmospheric pressure. Otherwise when the vent or valve is opened air may enter the piping system rather than being purged from it.
Watch out: some air bleeder vents come with instructions indicating that the vent cap is to be left shut, not open. Be sure to read the specifications and instructions for your air bleeder vent before making a change in the tightness of the vent cap.
Reader Question: Installing hot water heating piping air bleeder valves: leave the bleeder cap loose?
There is a lot of great information here. Definitely helpful for some things and the images are also a plus.
I have cracked one of the valves and an ever so slight amount of air comes out but not enough to get the water flowing. I'm guessing I may need to bleed all the water from the system and start from scratch. I'm just glad that it appears to be an air blockage and not something more serious.
Reply: it depends on the air bleeder valve type
Or use the alternative air purge methods at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
Finally, we can categorize air bleed valves on hot water heating systems into roughly two groups:
Automatic air bleeders, often including a float valve that drops to open the bleed valve to purge air when air accumulates in the float body - on these valves the manufacturer instructs to leave the valve cap loose so that the valve can vent automatically. An automatic air bleeder at the boiler or in a utility area should pretty much always have its cap left loose so that it can do its job.
At above left is an automatic air vent, the Maid O Mist No. 67 auto-vent. Instructions for this air vent are shown in the second photo (above-right) For a Maid O Mist No 67 auto vent, normally the vent cap should be left open one full turn from its closed position. If the valve is leaking water at that location you can close the cap to stop the leak (and prevent air venting) temporarily until you replace the leaky valve - a step that should be done promptly to minimize the risk of lost heat due to an airbound heating system.
Watch out: an automatic air bleed valve with a loose cap, installed on a heating baseboard in the living area, can present a risk of water leaks into the building floor (or ceilings below), if it's not inspected and if necessary cleaned or replaced.
In this location some heating techs and plumbers avoid the leak risk by just keeping the cap tight on the valve.
The valve won't automatically purge air (you are relying on other air purgers elsewhere in the system for automatic air purging), but it can still be opened and activated if necessary to purge air from the particular high hot water piping loop that it serves.
Manual air bleeders (photo at above-left), usually don't even have a cap, but might. These are kept closed except when in use.
Leaving the Manual Air Bleed Valve Shut: a tricky way to "shut off" radiators in older homes by not bleeding air out of the radiator
Sometimes in older homes the heating radiator control valves are stuck and cannot be operated. Usually the radiator valve will be stuck in the "open" position because no one wants to live with no heat in cold weather.
When we lived in a 100 year old home in Poughkeepsie, New York, ever fall we found that some radiators had become full of air over the summer when the heating system was off.
For a few rooms where we didn't want heat, and where the radiator control valve was "stuck" in the "open" position, we found that if we simply neglected to bleed air from that radiator it wouldn't heat up when the rest of the heating system was operating.
Over at RADIATOR VALVES & HEAT CONTROLS you'll see more photos of radiator control valves.
On all hot water radiators the heating control valve that turns the radiator on or off will be at the hot water inlet pipe to the radiator and may be located near the radiator top or bottom. There are a few air bleeder valves that have a tiny round handle, maybe 1" in diameter, but they will be mounted right onto the radiator body itself, not on the piping.
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.
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Frequently Asked Questions (FAQs)
Question: trouble getting the air out of an apparently air-bound heating system
We have a 2 zone hot water heating system that operates off of one thermostat. When calling for heat the 1st zone going to the 1st level of the home works good. The 2nd zone on the 2nd level has 6 baseboards and 3 seem to work good but 3 do not radiate heat at all. each one has a air bleeder on them and when I went to bleed the one off I got a little air but then got nothing, no water either. I it normal to have no pressure on them when not calling for heat or do I have an obstruction in the line such as frozen or some sort of dibree. - K.C. 1/27/14
the heating system is at my moms and I went over there yesterday to take a look at it and couldn't find a pressure gauge or not much of a place to put one with out taking apart some thing.
When I got there I had noticed that the water supply valve was shut coming from the water well going to the make up point of the hot water system and wasn't sure if that was suppose to be left open so I opened it and it sounded like it was taking some. Let me know if that is suppose to be left open or not or will it hurt something if I do. When I did have it on and went to bleed the air I found quite a bit of air but when the air stopped I didn't get water and if I shut it and waited al little bit I could get some more air but no water.
Shouldn't there be enough pressure on the system to keep on forcing the air out until you get water so maybe the bladder is bad or I need to add some pressure to it somehow. I did find out that it is a loop system and there is a 1" pipe looping along side the out side of the house between the floor and ceiling of the upper and lower level and pipes Ting off of it to the baseboards.
That is why we are still getting good heat at 2 baseboards at the beginning of the run and 1 at the end of the run but 3 in the middle you will get the one end of the pipe might be warm to hot but at the other end might be luke warm to cold. could there be a blockage in those pipes caused by sediment from the water? Or maybe the pump that moves the hot water isn't working right. Let me know your thought. Thanks for your time and help. - K.C. 1/28/2014
I cannot give safe advice about operating the controls on a heating system I can't see - there are just too many unknowns.
If the water to the boiler was shut off it may be that the system has ONLY a manual water feed. If this is hot water heat, (not steam heat) and if the boiler is not leaky, it may rarely ever need water added; if you pushed water in you may have overpressurized the boiler, which in turn can make the relief valves leak when the system heats up (another unsafe condition).
If on the other hand the boiler starting pressure was low, you might have addressed the original boiler pressure worry. But unless you bleed air until water comes out of the air bleeder valve, you have left air in the system - which can leave it air bound.
I think I would try forcing water into the system until I got water out at the air bleeder.
Then if I found I had too much pressure in the system, after bleeding out all the air one can always open a drain at the boiler to reduce the water pressure. (of course when you TOUCH an old part that nobody has touched for years it may break, leak or jam).
Watch out: for an old, not-working heating system that does not even seem to have normal safety controls and is in unknown condition, I don't think it's safe to keep fooling with it - you need to figure it's time to call a heating professional. We may try to offer some tips by email or online, but we are limited by your eyes - what you see and report. Often a pro will be able to home in on the no-heat problem almost immediately (that's a benefit of having a lot of experience).
Thank you for your help. The resent info was some good advice. I did shut the water valve off today and it didn't seem to set off any reliefs but I did notice that there was a bleeder on top of the bladder assembly and the cap was on and when I took it off it seem to bleed alot of air out and then seem to bleed it out in spurts like it was an automatic air bleeder and when it did that I could hear water moving through the pipes better and went upstairs and was able to bleed air out of one of the baseboard until it came onto water which hadn't been able to do before and one of the shorter baseboards that she said hadn't been working in awhile was working now. sounds like slowly but surly things are starting to work. I know it is hard to give info when not here looking at it but thanks for the info you have given. At least it gave me some knowledge and will call some one in if can't get things working safely and normal.
Sounds like progress. What's hard to determine from our conversation is to confirm that the system is air-bound (which I suspect) and whether you have found the bleed valves necessary to get that air out without having to call a heating service tech to force the air out of the system (using a pony pump at the boiler).
If you can keep bleeding air until water comes out at a bleeder that's what you want to do.
If you hear water moving through the pipes that was not moving before, you're making progress and we know the circulator must be working.
If you feel piping and it's hot for a ways from the boiler then is cold, that's probably where the air is blocking the system.
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