What is Radiator Bleeding?

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Radiator bleeding purges air that has accidentally gotten into the radiator's coils. All radiators must be bled on a regular basis, as the heating and cooling of water naturally releases air bubbles. You can try radiator bleeding if your heater seems to be functioning poorly or not heating as well as it did before.

A radiator works by heating water in a series of coils that effectively warms the air that comes in contact with the metal surface. When air gets in the radiator, it rises to the top and displaces some of the water. Air doesn't conduct heat nearly as efficiently as water, therefore it is both costly and wasteful to run your radiator with air trapped inside.

Experts on home maintenance and energy efficiency recommend radiator bleeding regularly at least twice a year. During the winter season when you use your radiator daily, or have to refill it with water, you may want to bleed your radiator more often. To evaluate whether there is air mixed with water in the radiator, turn on it on for a little while. Carefully use your hand to sense the temperature at the bottom third of the radiator. Compare this to the temperature on the very top of the heater. If there is a wide divergence, you should bleed the radiator.

The procedure for radiator bleeding is simple and safe. All radiators come with a notched fork, called a bleed key. There should also be a protrusion near the top of the radiator, on one side, called the bleed valve. Have ready an old rag, or even a small bowl, if you do not want water dripping on the floor. Fit the bleed key into the bleed valve and carefully turn it counterclockwise only a tiny bit, usually just a 1/4 or 1/2 turn. The air will start escaping with a hissing sound similar to a bicycle tire. When water begins to dribble out, all the air is purged, and you can gently return the bleed valve to its previous position.

If radiator bleeding does not seem to improve the performance of your heater, especially if several radiators in your home are malfunctioning, there may be another problem. A professional radiator inspector can detect whether sludge in the water is gumming up its circulation, or a mechanical component needs replacing. However, radiator bleeding almost always solves the problem.

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Discuss this Article

If you do not have a radiator key, a drum key will also work. That is, if you play drums or have a drummer in the family.
- anon24930
When I bleed my radiators, the only time water comes out is when they are hot, not just warm. Should I bleed them once a year or more during the cold season. If the temperature warms up and my heat goes down I have to bleed the air out again when I turn the heat up? Am I doing something wrong?

Why does this happen? I also have one radiator that no air or water comes out and it is never hot, just mildly warm. I never have to bleed my radiators on my first floor because they are always warm--should I bleed them anyway? My boiler is made by American Radiator Company. I cannot find a manual on how to care for it. Any suggestions? I don't understand the gauges.

- Mainedogg
You can usually find extra keys at a neighborhood plumbing or hardware supply store. They are not usually at HomeDepot. I believe you start at the top floor and work your way down when bleeding.
- anon23346
water keeps coming out of the radiator but no heat...We have been bleeding it for 1 1/2 hours...what is wrong here.
- anon22551
My radiators do not have keys. There is a key only on one of all of them.. I bled it so its good but the rest of them still have air trapped in them.
- anon20983
Hi. I think I've done my radiator bleeding terribly wrong. I actually bled some of the water out & now the boiler won't work. It switches on but then stops after 5 seconds & the light just blinks quickly. What should i do?
- darkforce
The hissing sound stopped but no water came out. How long do I wait for water to dribble out? And if it doesn't is something wrong?
- cathiefly
I have old hot water radiators, I would like to buy extra keys for them. where can I get them?
- anon6902
When I tried to bleed the radiators, a little water came out but no air (hissing sound). Do you think it still worked?
- pbloch
You can buy a new key at a hardware store.
- anon4796
I have a radiator that I need a long key about 6 inches. The id is 1\4 inch. Where can I find one that long???
- anon4496
Does a radiator need to be warm before bleeding?
- anon4300
I think I need to bleed my radiator, but I can't seem to find the key. Can you tell me where can I buy another one? My radiators are old and have been painted over, will it be difficult to bleed with a standard key?
- anon2957
Should the heating system radiators be bleed in any particular order, ie from first radiator on the heating run to the last or visa versa or from second floor to first or visa versa? The heating system should be turned off, but should the water be hot when purging the system?
- anon664
Can you buy any radiator key to bleed a radiator, or must you use one that came with the radiator?
- anon283

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