To get your landlady interested, point out that the radiators are filled with moist, warm air, and that the system is corroding from the inside, shortening the life of the radiators and clogging the boiler with rust. That means the boiler's life is being drastically shortened and may soon cause a massive expense. Fixing it now would be much cheaper than fixing it later. The question is, is she greedier than she is lazy?
As to what's actually the problem?
It seems to me that your apartment's system wasn't being replenished with water. Opening the radiator bleed valve wasn't doing anything because there was no additional water available to replace the air.
Central heating systems come in two flavours -- open vented and sealed -- and each refills with water in a different way. In an open-vented system, there is a tank at the highest point in the system, that uses a ballcock to fill up with water: see this diagram at diydata.com. The ballcock is in the feed and expansion tank. If the ballcock isn't operating correctly, the feed and expansion tank doesn't fill with water, and so no extra water will be available to fill your radiator. The ballcock could be stuck, or it could have been tied off so that some work could be done, and never untied. If you've got that kind of system, the fix would be to get the ballcock moving freely again. Is there some kind of maintenance area you could check out?
Alternatively, it may be a sealed system; there's another diagram showing that. These systems are filled up with a tap -- see the 'filling stop cock' in the other diagram. Normally, you'd check the pressure in the system every few months and use the filling stop cock to make sure the pressure is high enough -- say, 2 to 3 bar. Again, this will probably be very close to the boiler itself and so would need access to your building's maintenance area.
My guess is that it's a sealed system, and that the internal pressure has dropped right down to atmospheric pressure on the fifth floor. Lower apartments won't be suffering because gravity gives them more than their fair share of water, so most tenants won't suffer. However, any rust generated in your radiator will sink down into the system and clog it for everyone.
This is basically going to be landlord work unless you plan playing heating technician and checking the basement pipes. Here's the gist:
- Air vents on the radiator must flow air out so it can be replaced by steam to heat. They sometimes have adjustment valves on them so you can balance the system.
- Air vents that are producing a lot of noise are either
- too small of a vent
- clogged up / broken (this is you because you're leaking steam)
- Improperly designed systems can also push a lot of air out of the radiators. The steam delivery pipes should also have air vents on them before the radiators.
When working properly, those air valves should not let steam through. They should close when the steam reaches them, and open when there isn't steam. If there are showing visible steam, they need replacement.
I found this to be a good article on caring for steam vents that will provide more detail.
Best Answer
If you have permission to remove the radiator:
1) Make sure the system will not be actively producing steam.
2) Use a large open-ended or adjustable wrench to loosen the union between the brass radiator valve and the radiator. It will likely be difficult and you may need to tap on the union nut with a hammer or use a section of pipe to extend the leverage of your wrench to loosen it. The radiator is disconnected.
3) Use an open ended wrench and a pipe wrench to remove the brass valve. Spin the valve off with the open ended wrench while providing counter-pressureon the elbow with the pipe wrench. Only using one wrench may stress and crack the fittings.
4) Plug the pipe. Depending on which fitting you choose to remove, you may want a square headed pipe plug (if you have exposed female threads) or a pipe cap (if you have exposed male threads. Based on the photo, it looks like either a 1" or 1.25" pipe.
If you do not have permission to remove the radiator, but want to stop the hissing and heat... This is one-pipe steam, and either of the following options will solve two of your problems.
1) Turn your silver Hoffman valve upside down. This prevents the vent from venting.
2) Remove the silver Hoffman vent and replace it with a 1/8" pipe plug with a square head.