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A 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. 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. Contact Us by email if you are having trouble finding the information you need.
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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Why You May Need to Bleed Air from a Hot Water Heating System
If a hot water heating system develops too much air in the piping you may hear bubbling or gurgling in the heating pipes when the heating system is operating, or worse, so much air may be in the heating piping, radiators, or baseboards that heat may simply not circulate at all.
Here we explain how to locate, inspect, use, or replace automatic and manual air bleed valves on hot water heat, and we explain methods used to remove air from air-bound hot water heating systems by finding and repairing or using automatic or manual air bleeder valves, or by using two different service procedures to force air out of air bound pipes in a hot water heating system.
How to Open Manual Air Bleeder Valves on Heating Radiators and Baseboards to Bleed Out Air - step by step guide
Here we describe the procedure for using manual air bleeder valves to remove un-wanted air in a hot water heating system in order to correct noisy gurgling pipes or to correct loss of heat due to an air-bound radiator, heating convector, or section of hot water heating baseboard.
Step 1: turn on and turn up the heat. First make sure that your thermostat is calling for heat and that the heating system boiler has been running for ten minutes or so - to insure that the system is warm and up to normal operating pressure.
This step is necessary to ensure that heating system pressure will easily push out air from the air-bound radiator or baseboard, and to subsequently force hot heating water into the previously cold radiator or baseboard, confirming that you have successfully removed air that was preventing heat from rising into that unit.
In our photo, the room temperature (bottom scale) is at about 70 °F and the thermostat is set to 65 deg. F - in this condition the heating system will be off and removing un-wanted air in the system would be more difficult.
Step 2: find the air-bound radiator or baseboard: if you have not already done so, once the heating system is up to operating temperature and pressure, check each radiator, convector, or heating baseboard to see if it has warmed up. If you find one or more that remain cold, and provided that the cold heating radiator's valve is in the "open" position (counterclockwise), proceed to step 3 to see if that unit was air-bound.
Our photo (left) shows a manually-operated air bleeder on a heating baseboard.
In a building whose heat is delivered by hot water radiators or by hot water convector units every one of these may have its own individual manually-operated air bleeder valves installed.
If one radiator or convector is not heating up, find and open the air bleeder valve to let out air. Close the valve immediately when water begins to come out.
We hold a cup under the valve spout during this operation so we don't spill water in the living area. (Photo below.)
Step 3: bleed out excess air: Open the air bleed valve (turn it counter-clockwise) and listen for the hiss of escaping air. If no air comes out of the valve, just water, then the radiator or baseboard served by that valve is not air-bound.
A "roller skate key" like device may be needed to turn the recessed square end of older manual air bleeders on radiators and heating convectors.
But in pinch we've been able to open and close the valve using needle-nose pliers (photo at left) that have a point fine enough to reach into and grasp the square end of the valve control.
Step 4: close the air bleeder valve. When water begins to come out of the valve, close it.
Step 5: feel the heating pipes entering the baseboard, radiator or convector. Provided that the room thermostat is calling for heat, in a minute or so the pipes and radiator should begin to warm up and eventually become hot. If this does not occur either the heating system is off, there is another airbound location, or there is a separate problem with the heating system. In that case see HEATING LOSS DIAGNOSIS-BOILERS.
Other air bleeder valves are opened using a simple flat-bladed screwdriver.
But if the manual, screwdriver-operated air bleeder valve is badly corroded such as the one shown in our photo of a manual air bleed valve at the bottom of a heating radiator (photo at left) chances are it has been leaking and it be stuck.
This particular valve was one we handled with great care. If it was not easy to open and shut it again with a screwdriver (without much force) we'd have chosen to leave the valve alone until it could be replaced.
How Do we Know That the Air Bleed Valve Operation Has Been Successful?
What if there are no manual air bleed-out valves on my heating system?
If your hot water heating system has become air-bound (one or more sections of heating radiators or baseboards are staying cold even though the boiler is on and the circulator pump is running), and if your system does not have an air bleed valve to remove air blocking water flow, you probably need to call a heating service technician who will use one of the methods we describe at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE or at AIR BOUND HEAT SYSTEM REPAIR by PUMP.
It is also quite possible to add manual or even automatic air-purging devices onto existing hot water heating systems when and where they are needed (AIR BLEED VALVE INSTALLATION). Below we illustrate the two main types of air purge or bleeder valves: at below left is a float type air purge valve mounted atop an American brand air purger. At below right is a manual air bleed valve on a baseboard tee. [Click to enlarge any image]
But before rushing over to one of those cold radiator or baseboard fix-it articles, check the article summary at AIR-BOUND HEATING SYSTEMS to see if there is an automatic air purging device that needs repair or replacement on your heating system.
What if nothing comes out of the air bleeder valve when it is opened?
Reader Question: Hi - I have baseboard water heat. Nothing comes out of the air bleeder valves (All but one is manual, they fit a flat head screwdriver.) I just ran water through the whole system to get rid of all the air bubbles. The pressure on the little gauge looks good and pretty consistent. Now the pipes seem to be hot, but still when I open the bleeder valves I get no water and no hiss of air. Is this normal? Is it ok? Do I need to do something? Thanks very much for your informative articles. - Abby 10/7/12
If no water comes out of the air bleeder valves I suspect the valve body is clogged or blocked.
What if I can't open the air bleeders on some of my radiators
Reader question: The bleeding screw in some of my radiators have rounded off so cannot unscrew them. Can I buy replacement plugs and if so would they be simple to fit myself. Combi boiler system.
Maggie I have two possible solutions to rounded-off air bleed screw fittings.
First, try using a mini Vise-Grip tool that can reach inside the opening of the air bleeder and get a good bite on the air bleeder. I've successfully opened, bled, and closed tight air bleeders in this condition, allowing us to defer replacing the device.
The other solution is to shut down heat, cool down the system, and replace the entire air bleeder. Prepare the new replacement unit with teflon tape or pipe dope. Put down a towel, Remove pressure from the system (but you shouldn't have to actually drain it), work fast, and don't cross-thread the new fitting.
Question: can I change a manual air bleeder to an automatic one
Can an automatic bleeder be screwed in where the manual bleeder is on my radiator or will i have a puddle of water on my floor when auto bleeder starts working? - Darrell 11/20/12
Yes you can change a manual air bleeder to an automatic one provided you choose a device that works in the position in which you need to mount it.
You are correct to worry about unintended leaking, since most automatic air bleeders require (to work) that their screw cap be left loose. So it makes sense to use these conversions where someone will quickly notice if there is a leak, and to avoid them otherwise. In my OPINION.
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Frequently Asked Questions (FAQs)
Please see AIR BLEEDER VALVE DIAGNOSIS
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