Is this a steam trap?

where is this house located.
you do not want them working on that system.

try @offdutytech. I'm not sure he knows vapor systems but he at least knows enough to know when he needs to ask questions.

i live in ann arbor but grew up in clawson.

that is a big boiler, i bet it is very much oversized. the circulator i think is for a hot water loop somewhere, that is pretty common and fine if done correctly.

2.5psig is way too much for a vapor system.

does the radiator that won't heat that has the trap still have the vapor valve?

with the insanely high pressure it is very likely you have steam in the returns and that steam is closing the trap from the return side before the radiator can vent and heat. also possible the steam in the return itself is keeping the radiator form being able to vent.

feel the returns, they should not be steam hot. they may be hot but they shouldn't be as hot as the returns.

Yes, you do need a vaporstat for that system. The 0 to 16OUNCE per square inch variety, and set it to cutout at 7 ounces with a 4 ounce differential. That radiator that doesn't heat — it may be just fine, but that high pressure is blowing through the other radiators into the returns and will shut it off. The trap on it is a perfectly normal radiator trap. If it's not working, it can be repaired quite easily — but there's no point in seeing whether it's working or not until you get the pressure under control.

The control on the left is an aquastat —but where the wires go or what it's doing is quite impossible to say from the picture.

I hope so.
that’s why I asked

the pressuretrol has a cut in and cut out point. the cut out point is 2.5 psig and the cut in point is the cut out minus the differential so 2.5 psig -1.5psig which is 1 psig. The boiler fires until the pressure reaches 2.5 psig and once it shuts off it stays off until it reaches 1 psig where it turns back on. At least unless the system is huge I assume that is what happens. If the boiler matches the EDR of the radiators in the system then it won't build pressure but I suspect it it likely twice the size of the connected radiation.

Probably the next 2 things to look at are the piping at the ends of the mains and to calculate the EDR of the radiators.

Typically vapor systems just have one big vent at the boiler so that they can equalize the mains and the returns without filling the returns with steam although your system looks like it is missing that device unless there is some large cast iron device near the boiler that you haven't shown us. If the boiler return trap is missing then it will be completely dependent on the vaporstat to work properly.

The 1 psig cutin is still three times as high as your system is intended to run at…

You can put a regular radiator trap on that new radiator's return (like the "different" one you pictured) and it will work just fine.

There are no pictures of the return piping… so I can't comment on the presence of or placement of the main vent which the system needs.

I suppose, @109A_5 . There is a chance that the boiler is so closely matched to the radiation that it never ever builds pressure over 6 ounces or so. It has happened…

However. With the type of system we have here, if the pressure does go over that, all that happens is that you burn more fuel — and get no additional heat for your dollars.

Agree, however, I would do the due diligence. And analyze the system usage, like do they shut off radiators in unused rooms ? For the cost, I'd want to know if it is really needed.

Functional illiteracy on the part of the installers?

@mattmia2 said "it also has no swing joints so it could cause the boiler to pull itself apart."

@Jamiedle , that's the problem. Steel and cast-iron expand at different rates.

They look like Maid-o-Mist #1 vents (or one of their clones). I'd first measure the length and diameter of the steam mains, so we know how much air is involved.