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I have multiple radiators in my apartment, and all except one work. Unfortunately, it's the one in my bedroom! Brrr! The pipes to and from the radiator are hot to the touch, and I can hear water running through it. However, the radiator itself is not even warm except for the one fin closest to the pipe. Is there anything I can do to fix this?

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Do you know for sure that this is a hot water system? Sometimes steam can sound like running water. If it is hot water, there is a giant air bubble in the radiator preventing it from filling. It needs to be bled off by opening the small valve near the top at one end. You will typically need some sort of tool or key for this. Slowly open the valve. Along with the air, hot water will spit out, so be careful. When there's only water coming out you're done.

If it is a steam system, there is an automatic air vent valve on one side or the other about half way up, it looks vaguely like a small bell. It's clogged up for some reason, preventing air from being vented, meaning steam cannot enter the radiator. It either needs to be unclogged or replaced.

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The steam vent may be closed if it is adjustable. Some have numbers other just a cover that blocks the vent hole. –  mikes Dec 31 '13 at 12:46
    
I'm fairly certain it's a hot water system, as there is no air vent on the side and I see the bleed valve on the side opposite the pipes. I will try to bleed the radiator later. Are there any safety issues with bleeding them? Should I turn off the heat to the building before doing this? Or can I do it with the system still running? –  keladry12 Jan 1 at 23:27
    
The only safety issue is you could be encountering scalding hot air, steam, and water in the process. This is not a big problem as long as you are careful. Cover the valve outlet loosely with a rag to protect your hand while operating the valve. I've heard all sorts of "rules" regarding running or not, hot or cooled, what order to bleed multiple radiators, etc. I'm not convinced any method is much different than another. I think you will get a more effective bleed on a hot system and less sputtering if the pump is not running. Lowering the thermostat is enough of a precaution. –  bcworkz Jan 3 at 1:35
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