How do I Bleed a Radiator?

home garden

To encourage your heating system to work at optimum efficiency, it is important to bleed your radiators on a regular basis. Though it may sound difficult to bleed a radiator, it is actually quite easy to do. There is no special training required. All you need is a radiator key and a small bowl.

If the heat in your home isn’t circulating well or the bottom portion of your radiator is warm, while the top portion is cold, there may be air trapped inside your radiator. When air gets trapped inside a radiator, it reduces the radiator’s ability to heat effectively. This trapped air may even lead other parts of your heating system to function poorly. Sometimes, most of a radiator will fill with air. In such a case, there will be no noticeable temperature difference. The whole radiator will be cool to the touch.

As you prepare to bleed a radiator, you will most likely be starting with a system that has been turned on. As such, there should be warm water in the radiator. Before you begin to bleed a radiator, you will need to turn the central heating system off.

To bleed a radiator, you’ll need to have a bleed key handy. With this in hand, locate the bleed valve. It is typically positioned at the top of a radiator, near the end. Insert the bleed key into the bleed valve and turn it counterclockwise. Don’t turn it too much; a half a turn is usually enough to successfully bleed a radiator.

As you turn the radiator key, the valve will open and you will hear a hissing sound. This is completely normal and is simply caused by the air escaping. Once water begins to leak out of the radiator, it is time to close the valve. To do so, turn the bleed key clockwise for half a turn. You can then move on to bleed a radiator in another part of your home, as necessary, before turning your central heating system back on.

When you bleed a radiator, keep a small bowl or rag handy to catch the water that drips down. If you have a sealed heating system, be sure to do a pressure check and add water if needed. Once you’ve done so, you are finished and may turn your heating system back on. Store your bleed key until the next time you need to bleed a radiator.

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29
My radiators downstairs are cold in the middle and bottom but piping hot at the top and the overflow pipe has sprouting water for the past eight months. Please, any suggestions on what i could do myself would be most apprdciated. thank you.
- honeyb
26
My central heating is not working after bleeding some radiators.
- anon26485
25
I have an old radiator heating system. I've bled the radiators and got water out immediately. Problem is, the bottom 3/4 of the radiators are cold - only the top is hot. Any suggestions on how to fix this problem?
- Lwedenbine
24
My downstairs radiators are always warm. On my second floor I have to let the air out of the radiators many times during the winter?? If the heat is turned down and then back up that is when I have to let the air out of the ones on the 2nd floor. I have an American Radiator Company boiler system--can't find anything about them. I don't understand the gauges. I do have a closed water system and rarely have to add water. I would like to know proper maintenance on my system.
- Mainedogg
23
I live in an old row house with cast iron radiators. When I bleed the radiators, I get air from two of them (top 3rd floor and water from the others (the heating system is on). What could be the problem and should I add water to the system? If so how? How do I check the pressure and what should it be.
- armond
22
hi, we are bleeding the radiators in our home and the one's on the 2nd and 3rd floors are remaining cold. any suggestions on how to fix this problem and make them warm?
- liljen10
20
I have an old house with iron cast radiators. How do you bleed these? I took out the pressure valve, no water came out. Is there another place on them to bleed? Some of them turn on and other don't. Can you give me some suggestions?
- Loydaf
19
Ok, I went to bleed my upstairs radiators and all that came out was air,...no water. Is that because the water only rises as it is heated ? or what? I read that when I turn on my boiler that the gauge should read 10-12 psi (which it did when I turned it on) but I dont want to turn it on and let it run to build pressure and then "bleed" it to see if water comes out. I'm afraid it'll blast out way too fast and way too hot.

I checked the valves coming out of the floor and they are all the way open. I guess I need some help here,..any answers or recommendations ??

- bussbass
18
If nothing comes out when you turn the key that means that you need to re-pressurize the system by adding water at the boiler. There should be a valve that you can turn on and a pressure gauge at the boiler to tell when it is re-pressurized.
- anon20127
17
Hello wiseGeek. I have managed to thread one of the bleed valves, so I can't bleed the front half of the radiator - any suggestions? Thank you
- thisisbam
16
I dont know what a bleeding key is????
- anon18888
15
After bleeding all the radiators in the flat, I switched on the boiler but non of the radiators seems to be heating up and I find the boiler makes some terrible noise on and off. What do I do next?

Josie

- anon12273
14
i was wondering when bleeding radiators how much water should you take out ?
- anon7253
13
thanks. I'll give it a try.
- cpslot
12
Look where the main water supply comes into your house. Follow the pipe that leads to your boiler. Somewhere along there should be a ball valve where you can shut the water feed on & off. On ours, just after where that valve is there is a regulator..(not sure what you call it) It's about the size of a large grapefruit. That is what I tapped with a wrench. Once I did that,the water ran in. If you placed your hand around the pipe you could feel the cold water feeding in. Hope this helps you.
- Shelzbells
11
Shelzbells: Where do I find the auto water feed? And congrats!
- cpslot
10
where do i buy old radiator keys?
- slewis5272
9
I finally fixed mine!!! The auto water feed was turned on but must have been stuck, I took a wrench and banged the valve once and it immediately then filled up. I then went back upstairs and opened the valve on the cold radiator. ALOT of Air gushed out, and after 10 seconds or so, water also came out. Now all of them are working normally.
- Shelzbells
8
The second floor radiators are cold and when I bleed them I get some air but water never comes out...what should I do?
- Erush
7
I am having the same exact problem as cpslot, I get water from almost all of them. 2 are cold and only a small amount of air comes out, but no water. another is hot but no water comes out. Is water supposed to fill them automatically?
- Shelzbells
6
I have an old 3 story house with hot water radiator heating. the ones on the 1st and 2nd floor are hot and when I bleed them, water comes out. The 3rd floor radiators are cold and when I bleed, I get some air but water never comes out...what should I do?

Phil Murphree

- philmurphree
4
i don't have central air-so does my thermostat heat need to be on or off?
- jomama92371
3
must water flow before I turn off the key? What if there is no hissing sound?
- anon4369
2
I live in an old row house with cast iron radiators. When I bleed the radiators, I get air from two of them, and water from the others (the heating system is off). Also, I get nothing at all from another radiator. Any thoughts? thank you
- cpslot

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Written by N. Madison
Last Modified: 25 August 2009

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