There is probably more than one loop.

Best guess would be that there is air in the pipes, preventing circulation of the water, or a circulator isn't working.

Time to call the association.

So you think there could be more than one loop serving each condo unit?

Is it water circulating or steam? I had thought it was steam.

For some reason tinypic is down and not showing pictures.

Let's try this:

If you have steam, there should be a vent at the top of the radiator. It could be non-functioning. Repost under a steam question and kalining will respond.

If the condo is the size of one floor of a house, you may have your own loop. If you have steam heat, with a non-functioning steam vent, then you could have heat in some radiators and none in others. If you have hot water heat, it's unlikely that you'd have non-functioning radiators on the same loop.

The radiators don't have any external vent/valve/anything. They are painted shut so I can't get inside without cutting it open. When I look into the openings at the top I just see fins, no devices.

Edit that last post, after a lot more inspection with a small dentist's mirror, I can see some type of device sticking up inside. On the top of it is a little thumb knob.

If they are hot water units they are probably full of air.
There should be a bleeder on each radiator.
Open it until water comes out.
Be prepared for oily, smelly water.

How do I tell if they are hot water or steam?

When was your building built?

If it's pre WW II it could be steam, but the pipes don't really look big enough to be steam, although it's tough to tell.

If it is steam, it's a closed-loop system given that you say you have supplies AND returns. That could mean that there are problems with the steam traps on those radiators.

But, the fact that you have a quarter turn valve is a pretty good indication that you have hot water heat, not steam.

It is very possible that you have separate loops supplying your radiators. I lived in DC in the early 1990s in an early 20th century 5-story building. The front half of my apartment and the back half of my apartment had separate loops.

That little thumb knob is likely the air bleeder. It could be that your radiators need to be bled, but given that you have zero heat in several radiators I think it's more likely that that loop isn't functioning.

Talk to your building maintenance people. You might find that they heat is being brought on in stages, or there could be a problem with the circulator on the loop supplying those radiators.

I was able to get the bathroom opened, here is a picture of what's inside. All the rest are of the same design so I assume they look the same, only bigger.

If the picture doesn't work, let me know.

kframe19, the building was built in the late 50's.
-I believe I have supply and return, I assume the pipe on the right is the return, but I don't know much about it.
-The black knob on the bottom left hand side is what can be reached when the cover is on, I assume this is for the homeowner to regulate the heat. It only turns 1/4.
-The odd thing is that hot radiators vary on the side of the building, half on one side are hot, half on the other side. If it is 2 separate loops for my unit, they did some pretty intricate staggering.
-Not only is there a little thumb knob, but there is a valve underneath it, I believe you could see it on the right side of my picture.
-There really isn't building maintenance, just a part time grounds keeper who lives in one of the units. Any work needed to be done to something like the HVAC would require an outside contractor to be called in.

Thanks for the help everyone!

Maybe this will work:

{{!gwi}}

It looks like a hot water setup, but I can't be sure. On the top right of the radiator is an air vent, but the valve below it is shut. If you open that valve, you'll bleed the air out, but the vent may not be automatically shutting, hence the valve is in the closed position.

Loosen the cap on top of the air vent and open the valve, if you can, and first air and then water, should come out. It will be HOT, so work safely and be prepared to shut the valve quickly.

So that thumb valve should be automatically shutting? But since it's not, that's why someone closed the valve underneath it?

Please bare with me, I know nothing about this.

I will open the vent as you said, should I wait until midday tomorrow when the heat will probably be off? Or should I do it while the heat is on?

The valve is currently closed. The position is in the horizontal position. In a vertical position, the valve will open and allow air to move upward to the air vent, which has a bicycle tire type valve under that chrome cap.

You can close the chrome cap and open the valve below it. Then slightly loosen the cap and allow the air to escape. This will only take a few seconds. The air vent is not supposed to leak and the cap can be left slightly loose and the vent will continue to bleed air automatically without your intervention in the future.

Someone closed the valve, probably because the air vent was leaking. With the valve closed, you can remove the air vent and replace it. If the hand valve is bad, the pipe to the radiator will have to be shut off in the boiler room.

You can do this while the heat is ON, but you only want to loosen slightly the chrome cap on the air vent. This will allow air to escape and only a dribble of water will come out until the air vent seals itself, providing it's working properly. If it doesn't seal up, you'll need to tighten the cap again and either replace the vent or manually bleed the radiators when they don't work.

The hand valve on the bottom left should move more than 1/4 turn. But anyway, don't use more than moderate pressure to move the various valves and parts described above. If you break one of them off, you will have water coming up from the boiler into your apartment floor.

Another point, under the chrome cap you will see a bicycle valve stem. If the air doesn't bleed by itself, you can depress the center of the stem with a blunt object, but be prepared to immediately put the cap back on in case the valve sticks.

If you look at the last picture I posted, closely at the hand valve at the bottom left hand corner, you can see a peg sticking out the back of it. That peg hits a solid piece of metal on the valve body, and stops the valve handle from turning more than 1/4 turn.

I did as you said, I bleed all the heaters and it works great! I appreciate the help!

One problem I had is that some of the valves under the air vent did not work when I turned them. I notice a spring on the other side of the handle so I gently pried the handle away from the valve body and air came out. Soon after water started coming out so I let it go, the water stopped immediately. The air and water were coming out from around the valve, not the vent on the top. Those radiators work perfectly now. I just wonder what that was all about...

Somewhere along the line, somebody worked on the system and didn't bleed out all the air. Since air goes UP, it all came to visit you.

I'm glad that you're warm again.

The funny thing is that I actually don't like it warm, I like my home to be relatively cold. There are a lot of old people in my building and on the association board so they have the heat going pretty high.

I plan on keeping 1 radiator off for most of the Winter and 2 others about halfway closed. Any problem doing this? Will it result to more air in the radiators?

No problem at all doing that.

The quarter-turn simply impedes the flow of water through the heat exchange unit. Less hot water flow, less heat into your home.

It won't have any effect at all on air getting into the units.