Mysterious cold radiator

aat879

We've lived in our single-family house for several years. I've become a well-informed steam heat user, so I understand most of the basic principles, e.g., that if air can't get out steam can't get in. Ours is a one-pipe steam with two main brances. The boiler is near new and was properly sized by the local steam expert with proper near-boiler piping (drop header, etc.). Pipes all insulated. The system runs great, though still trying to dial in the far radiators with the right air vents to balance the system perfectly.

The single radiator in our small den, however, is a mystery that driven me nuts for a couple of years. I want to solve it this winter so we don't need to use a space heater. This radiator is on the first floor about halfway down one of the main branches. At the beginning of the heating season, when everything is really cooking, it gets nice and hot. But then, when the system is maintaining temperature, it pretty much goes cold. It'll occasionally get just a little warm, like it's really struggling, but then go cold when the cycle ends. The radiator immediately before and after this one on the same floor get really hot with each cycle. For the life of me and I can't figure out why this radiator just poops out.

I thought it might be an air vent thing, but I tried putting on a Maid-O-Mist with the largest venting capacity and faced the same problem. When I go down and feel the riser (where the pipe leaves the main), I can feel good warmth through the insulation until I get to the elbow that turns up toward the radiator above.

Any ideas on what's going on? I can't imagine it's anything other than trapped air, but I have no idea how to determine whether that's so and, if so, how to get it out. Perhaps there's some debris blocking air, but I'm not sure how to determine whether that's so. Appreciate any help.

EdTheHeaterMan

The pitch of the pipe that is feeding that radiator may be incorrect. If there is a sag in the pipe then condensation that is trying to return to the boiler may be trapped in there partially blocking the path for the steam to get to the radiator. Look close at the pipe between the main and the radiator to see if the horizontal pipe maintains a constant pitch of 1" per 10 feet sloping downwards from the radiator to the main.

There are stories about how a home owner used the steam pipe to hang a heavy bag for working out or using it to hang all kinds of stuff like a swing for the 4 year old. When the kid grew up to be 16, and weight in at 190#, the radiator stoped working.

Long Beach Ed

Check what Ed said, of course. You can also have a problem with the angle valve. They can fall apart internally and cause a restriction. And of course the pitch of the radiator. If I were troubleshooting this, I would use air pressure through the 1/8" vent connection into the radiator to see that the line was free of restriction. I'd pump with a hand pump and listen for gurgling or feel for blockage. The pressure in reverse direction would also quickly identify a disassembled valve face.

I'd also check my boiler sizing. This can be the problem with newly sized boilers. If the boiler isn't providing sufficient steam, it's possible that one radiator would remain cool. The ones condensing the most steam will draw more steam into them, while one on the sideline could go cold. Since the vents aren't closing on short cycles, there's no "encouragement" for steam to find that radiator. Fast vents in all the other radiators will not encourage steam to find this one.

Try removing the vent from the cold radiator while closing one or two of the bigger ones. See if it heats up then. Unless there's some mechanical or condensate restriction, that will narrow your diagnosis down to venting. I'd use American-made vents, to remove Chinese defects from the equation.

aat879

Thank you both.

EdTheHeaterMan: I should have mentioned it, but what you mentioned was one thing I thought might be the culprit and did check it. The pitch is pretty much perfect, so that's ruled out. Pitch of the radiator is also correct.

Long Beach Ed: Pretty positive the boiler sizing is not the issue. The boiler is definitely producing enough steam. I've put vents with the smallest venting capacity possible on each of the radiators. The close ones have super slow vents so that they don't in steam too fast (and cause the room to boil). I have had to increase the venting rate on some of the farther radiators in order to balance things out, and all of those work well. It's just this one that is really struggling if working at all.

I've also been suspicious of the supply valve (that's what you mean by angle valve, right?). The issue is that my radiators are actually convectors recessed into the wall. They look beautiful, but this also means I don't have full and easy access to repair/replace the supply valve. Please see the picture to get an idea. Is it possible to remove and replace the valve from the convector cutout? Pretty sure I'll need to remove trim to get a wrench in there, but perhaps there is a way to do the job in such a restricted space.

First I'm going to fiddle a little more with the vent to try and rule that out.

Convector 1.jpg

Convector 2.jpg

BobC

You could try removing the air vent on that convector and then turn the system on, make sure someone is standing buy to shut the system down if steam comes out the vent hole

There may be a short horizontal pipe under the floor that is not pitched right. Does the radiator shutoff valve get hot or at least warm?

Bob