I have gas powered hot water heat in a home I purchased. When I tested it this morning I got a lot of whistling and other noises that subsided for the most part. After the heat had run for 20-30 minutes, I checked it radiator in the house. All the radiators were at least warm, with the exception of one of the radiators upstairs.

What could cause this single radiator to not get warm at all? I noticed slight temperature variances between the other radiators, but this one seemed to not be warm at all. I assume it should get warm if the hot water is flowing through it, and I also assume the hot water must be flowing through it to complete the circuit. So, what gives?

  • Heat being lost before it gets there? Closed valve? – keshlam Oct 12 '16 at 23:28
  • @Keshlam could the system function with a closed valve? More specifically are there multiple loops in a typical system allowing hot water to flow around a radiator that has a closed valve? – Brian G Oct 12 '16 at 23:38
  • @Keshlam to your other point about heat loss, that seems less likely, given the room next to it has plenty heat, and this is, I assume, the original radiator system. – Brian G Oct 12 '16 at 23:39
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    Air. Did you bleed the radiator? There's a square bleed valve at the top corner of each radiator; turn it - with the correct tool - until water runs out, then close. Repeat for all radiators. It's usually the highest radiator that's affected. – PeteCon Oct 12 '16 at 23:57
  • @PeteCon now that I have done a little research that seems very plausible. It's not clear to me how the air gets trapped in only one radiator, but at any rat,e I will get the tool and give it a shot. I think I will bleed all of the radiators as I assume this is a standard maintenance procedure. – Brian G Oct 13 '16 at 0:06

Air. Bleed the radiator. Air can very, very easily be trapped in one radiator, which will cause it to not heat.

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In case you have not solved the problem, here are a few ideas/suggestions. Is this radiator the only one on this floor? If it is, try to measure from the top of this radiator to the pressure gauge on the boiler; (you do not have to be exact). Divide this measurement by 2 to get the approximate boiler pressure with the boiler off and the water cold. A rule of thumb is: one story above the basement 12 lbs., two story 15 lbs., three story 20 lbs. The cold pressure on the boiler must be sufficient to hold a column of water up to the top of the highest radiator. Another indication of a high enough pressure is when you vent the radiator as someone suggested before, do you get water out of the vent. If you do the pressure is OK. does this radiator look the same as the others in the house. Could it have been added later. If you think it was added later or looks different than the other rads send a picture of this rad. There are some rads that are steam only and will not work with hot water heat. There are other possible problems/solutions.

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