Hot Water Heat Air Bleeder Valves

Guide to Air Bleeders for Radiators, Baseboards, Convectors

Hot Water Heating System Air Bleed-out Procedure

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 above shows a manually-operated air bleeder on a heating baseboard.

We start bleeding air out of the system at the air bleeders closest to the cold radiator or baseboard; the air bleeder we want is usually found at the "downstream" or "high" end of those heaters.

Manually operated air bleeder valves are opened (turn counter-clockwise) using either an air bleeder valve key (if the bleeder valve stem is square) or a simple flat-bladed screwdriver (if the air bleeder valve stem is slotted).

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.

A "roller skate key" like device called a radiator air bleeder valve key may be needed to turn the recessed square end of older manual air bleeders on radiators and heating convectors.

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.

Where to buy a radiator air bleeder valve key

2016/10/19 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.

Reply:

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. Air bleeder valves are also sold by local plumbing suppliers, by building supply stores such as Lowes and Home Depot, and from online plumbing suppliers.

Below you can see a typical radiator air vent key or "radiator air bleeder key" produced by Durst.

Slotted type air bleeder valve stems use a screwdriver to operate the valve. They're often sold under the description "Coin Air Vent Key Bleeder" but as the slotted valve stem is usually recessed you may find that a coin doesn't work well.

Watch out: If no air comes out of the air bleeder valve valve, just water, then the radiator or baseboard served by that valve is not air-bound.

If nothing comes out of the air bleeder - no air and no water, the system may not be hot enough or it may be air-bound.

See NO AIR & NO WATER COMES OUT in this article just below.

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.

Separately at AIR BLEEDER VALVE FUNCTIONS you can see photos of all of the various types of hot water heating system air bleeder valves including both manual air bleeders and automatic or float-type air bleeder valves.

Watch out: 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?

• If you open a manual air bleeder valve on a hot water heating system and air hisses out, there was air that needed removal. If only water comes out, that device was not the one that is air bound.
• If the heating boiler is already running and hot, quite quickly, in a minute or three, the radiator or convector that was air bound will get hot to the touch. Feel first at the pipes that enter the radiator, convector or heating baseboard since that's where hot water will begin entering the previously air-bound device.

What if I Open the Air Bleeder but Nothing Happens: No Air & No Water comes out?

Photo at left: a Taco air scoop with an automatic air purge valve on its upper right tapping. This is an effective position for a float type automatic air bleed or purge valve.

If no air and no water comes out at a vent your heating system may be air-bound AND at the same time you have to correct one of the following conditions:

1. Temperature & Pressure inadequate
   
   The heating boiler and hot water throughout the system have not been run up to normal full operating pressure: somewhere between 20 and just under 30 psi in pressure and somewhere around 180°F to just under 200°F for a residential heating boiler system.
   
   Without adequate pressure in the system, particularly if you're trying to bleed air at an upper floor in the building, there simply may not be enough pressure to push heating water (*and air) up to that level.
2. Circulator pump or zone valve off or closed:
   
   The circulator pump s not running or a zone valve (if present) controlling that heating zone is not open
3. Closed heating line valve or a closed radiator valve
   
   where you're trying to bleed air. Be sure that no control valves or radiator valves have been shut on the heating zone invovled.
4. Bleeder Valve Clogged:
   
   The air bleeder valve body itself may be clogged or blocked with sediment or scale.

Watch out: First though, be sure that the thermostat is calling for heat and that the system is up to full operating temperature. That alone may put enough pressure in the system to successfully bleed air out of the cold radiator or baseboard.

If even after the heating boiler has been running for ten to fifteen minutes and is up to full temperature (burner has cycled off) you still get nothing coming out of a radiator or baseboard air bleed valve then your system is probably air-bound.

At that point you need one of the two air-bound heating system repair approaches described by the two blue links just below.

An InspectApedia reader noted:

If your hot water heating 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. 11/27/2014 Anonymous

Reply:

Anon

Good point and thanks for the comment.

1. Double check to assure that your boiler is up to full temperature and pressure. Pressure needs to be between 20 and just under 30 psi.
2. Check that circulator pump(s) are working and if present, that zone valve(s) are open

What if there are no manual air bleed-out valves found 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

that describe two more aggressive methods to get past an air-bound hydronic heating system when the bleeder valves alone won't do the trick.

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.

Below we illustrate the main types of air purge or bleeder valves used on hot water heating systems

Just below is a float type air purge valve mounted atop an American brand air purger.

Next, below, is a manual air bleed valve typically found on a pipe elbow at the higher end of a baseboard run.

Below I illustrate a typical air bleeder valve on a heating convector.

And finally, below is a beautiful manual air bleeder valve on a hot water radiator.

See AIR BLEED VALVE INSTALLATION

The air bleeders didn't work to get all the air out of my heating pipes; what else can I do?

Air bleeder valve on a new furnace (1 yr old ) has not remved air from system? What can I do ? On 2020-12-24 by Jim Zavislak

by (mod) - there is indeed a solution

Jim

If replacing or at least opening and chekcing the air bleeder valve doesn't do the trick then the system is airbound somewhere else in the piping rather than close to the bleeder valve.

In that case you can use the procedure that we describe at

AIRBOUND HEAT SYSTEM REPAIR BY PUMP

Air Bleeder Not Working? Only Water Comes Out, No Air!

Only water comes out at the air bleeder but the radiator is still cold

What if i open the bleeder and only get waters but the register still doesnt get hot? On 2018-10-11 by Dan

by (mod) - possible causes of no air coming out at the air bleeder or vent device

Dan

There could be one of the following cases

- The heating system is not hot and therefore not up to full operating pressure

Turn the thermostat way up and be sure that the boiler runs and that the boiler pressure on its pressure gauge is between 20 and just under 30 psi (for a typical residential building)

- The circulator is not working or a thermostat has not called for heat at the zone involved

Be sure that you've turned up the thermostat and fully heated and pressurised the heating zone in which you're trying to remove air

- You are too far ahead of the air - The air block in the heating system piping is well before the point at which you are opening the bleeder

Look for an air bleeder on a heating line, baseboard or radiator that is back closer to the boiler

Still no air coming out?

- You may need to bleed more water - there may be quite a bit of water between your point of bleeding the heating piping and the actual air blocakge

- You may need to use one of our two more aggressive methods to remove air from the heating system:

at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
or

at AIR BOUND HEAT SYSTEM REPAIR by PUMP.

- The heating system may not be airbound: look for a failed circulator or circulator pump or a control valve that is closed on that heating zone, radiator, or baseboard loop

How to Replace a Broken or Defective Air Bleeder or Vent

Steps in replacing a broken air bleeder valve

Hi, my son has a convector radiator in his bedroom which desperately needs bleeding, however the inner part where you enter the key has broken off so I'm unable to turn to let out air. Can anyone please advise whether it's still possible or whether the radiator would need new part? 2016/10/27 Nicci

Reply: how to replace a radiator air bleeder valve step by step

Nicci,

In an emergency, such as over a holiday weekend when your son is freezing to death and all of the heating and plumbing suppliers are closed, one could bleed air by removing the vent entirely, then screwing it (or a pipe plug) back into the opening when water appears.

The air bleeders on radiators are rather standard in thread and dimension. You can simply replace the bleeder device by unscrewing it and screwing in a new one with a bit of pipe dope or teflon tape.

BUT first you'll need to let the heating system cool down and you'll need to drain enough water from the system that you don't have a flood from water squirting out of the air bleeder opening during the repair.

Air bleeder valves are described in detail at InspectApedia in this

article AIR BLEEDER VALVES

Here are the steps that a heating service technician would follow - more or less, as we don't know a thing about your specific heating system

1. Turn off the boiler
2. Let it cool down
3. Turn off water supply into the boiler
4. Drain water until the pressure drops down to maybe 0-5 psi. You do not need to fully drain the system, just drain enough that there is no water pressure.
5. Prep the replacement bleeder device so that when you unscrew the old one if water comes out anyway you can minimize the mess by acting promptly to place and screw in the new one.
6. Place a bath towel on the floor where your flood is going to occur (maybe)
7. Unscrew the bleeder device - DO NOT PANIC if water starts coming out. Keep calm, carry on.
8. Screw in the new air bleeder device - don't panic or you may cross thread it
9. Mop up the water
10. Take a deep calming breath
11. Turn the water supply to the boiler back on
12. The pressure/reducer/water feed valve should automagically refill the boiler to the proper cold-starting pressure.