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All radiators are heating except one, so I'm trying to bleed it. There doesn't seem to be an obvious bleed valve (unless it's that nondescript, frozen, simple bolt on the top front corner of the left end of the radiator). I'm trying to determine whether my system is steam or hot water. I have read/viewed multiple online articles and videos, but this all seems inconclusive to me.

It's a two-pipe setup, with the apparent inlet at the top of the left end (this pipe is warm) and a valve at the bottom of the right end (this valve and pipe are cool). Pipe at top would suggest hot water (right?), but a plumber once told me my system is steam. I take statements like this with a grain of salt, however, since a contractor also once told me my boiler runs on heating oil when I know full well it's natural gas. Furthermore, the internet seems to say that a steam system's radiators will have air vents halfway up on one end of each, yet mine do not; and the valve styles are mixed (some are cylindrical while others are globe-shaped).

Since the radiator characteristics have not definitively answered this question, I also looked at my boiler. Here the apparent lack of a sight-glass and the presence of an expansion tank seem to suggest that it is — or at least was — a hot-water system. But if this truly is HW, then where are my bleed valves? And why did the plumber who once did work on the system tell me it was steam?

I think the boiler was originally oil but was converted to NG, so maybe the radiator system was converted from HW to steam? The house was built in 1920 and the boiler is old as the hills. Any help untangling this mystery is very much appreciated.

radiator  right end

radiator left end

boiler

EDIT TO ADD: Here are a few close-ups.

bleed plug? close-up

bleed plug? close-up

boiler close-up

boiler close-up

temp & pressure

More pictures, January 23:

radiator full length

boiler

boiler

boiler

boiler

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  • Nicely done for your first post! A closer look at the black valve in the first pic would be most helpful, as would any make/model info from the boiler itself (even though it's as old as the hills, there may be someone here who knows something about it). – FreeMan Jan 22 at 17:53
  • I've added a few "better" photos to the end of the question. It's hard to get good shots of the boiler because the closet is so cramped. And I'm a crappy photographer. ;-) – Bill Martinson Jan 22 at 19:35
  • Grab a closer picture of the gauge with two needles on the boiler (the pressure/temperature gauge) which will remove all uncertainty with regard to steam/hot water, not that there's much. That is a war-horse of boiler that's been through a few changes - I can't match it up with online information at New Yorker boiler, but I would not be surprised if it started life as steam / oil and is now gas / hot water. The overly complex piping probably grew up organically as things changed over time. – Ecnerwal Jan 22 at 20:13
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    Photo added. Caught it while the thermostat had it running; looks like about 122°F and 16 psi currently. I'm guessing the gauge going up to 320° suggests it originally intended to accommodate steam. – Bill Martinson Jan 22 at 20:26
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    "Overly complex piping" indeed. My photos barely show the half of it. ;-) – Bill Martinson Jan 22 at 20:27
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That's hot water. Not a great picture, but there's a circulating pump barely visible, as well as the other factors you have noted.

In your second picture, the bleed valve is the black thing to the right of the water inlet, on the corner. Takes a flathead screwdriver as best I can tell from the picture.

enter image description here

There's also at least one automatic bleeder visible at the boiler.

enter image description here

If you have children, you will want to clean up the peeling white paint, which is very likely to be lead-based.

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  • You're right about the flathead bolt. I tried loosening it, unsuccessfully. The groove on the head is too large for any of my screwdrivers to make a positive lock without slipping out, so I'll need to buy a different tool. Is it safe to try to loosen this with WD-40, or will that work against getting a good seal when I tighten it again? – Bill Martinson Jan 22 at 19:09
  • I added a few closer pictures to the question. I've tried again to loosen that bolt but it's pretty stuck. What's the safest way to loosen it? – Bill Martinson Jan 22 at 19:49
  • WD 40 (despite the common misconception) is not optimized for breaking free rusted stuff. It's "Water Displacing" - PB-Blaster, Kroil, or Liquid Wrench would be a better bet. None of those should affect the seal - but if the slot is that worn, you might want to think about replacing it eventually. – Ecnerwal Jan 22 at 20:17
  • Thanks for the recommendations. Soaking in PB Blaster now. – Bill Martinson Jan 22 at 22:12
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First off, that is definitely a hot water heating system. As for the thing with the screwdriver head, do not remove it or try to loosen it. "IT is not a vent". It is a pipe plug. If you remove it you are going to get very wet. As for that boiler, it probably is not very old as far as hot water boilers are concerned. They last until they crack a section or casting which can be as long as 100 years or more. I have seen them last that long. Where is this boiler installed in the building. Is it installed above the radiation. Is it in an upper floor with the radiation below it. I ask because it looks like a down fed system and if it is, that may be why that rad does not have a bleeder or air vent. More information is needed as is a picture of the boiler and piping. (pull the camera back to expose more of the boiler and piping). Looking at the radiators, they look to be piped as a down feed system with the top pipe as the inlet and the valve at the bottom the outlet.

A bit of education, the only difference between using the boiler for steam or hot water in boilers of that design is the boiler's trim. This type boiler can be either steam or hot water depending upon the trim used. Also they can be fired with your choice of fuels, any oil or any gas.It depends on the burner installed.

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  • Definitely looks top-fed to me too. It's difficult to get good pictures because the closet is so small. I cannot pull the camera back any further because it's already up against the wall. I've tried to get some others in selfie mode, and today I added a few more pictures to the question above. I can take more specific ones if I know what you need to see. – Bill Martinson Jan 23 at 19:25
  • you can put a mirror on the wall and shoot into it to get further back... – dandavis Jan 24 at 10:24
  • What other pictures would be helpful to post? – Bill Martinson Jan 26 at 18:08
  • Oh sorry, when I posted those additional pictures I forgot to answer your question about installation. The boiler is installed on the ground floor, same as the radiator that's not working. But I do have a second floor with several radiators on it, and most/all of them I believe have the same top-mounted pipes on one end (the ends without the valves). – Bill Martinson Feb 1 at 15:19

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