radiator question

There is no reason why you should never turn it off. The handy man is wrong.

Yes, the radiator needs to be bled.

Ishtar wrote: It would be great to get an answer to this. In my previous apartment the radiators would make a really loud knocking sound when we turned them off. I have no idea why. Was it condensation, maybe?

It was likely that the valve was not able to close completely thereby trapping water in the radiator but letting steam to continue to push through the opening.
Radiator valves aren't meant to be used on a daily basis. After a while the only way to turn them off is to put a pipe wrench on the stem since those plastic handles break apart when any excessive force is used.
OP's handy man has another problem besides replacing gaskets and packing in the abused valves however. Once tenants start opening and closing radiator valves at their leisure it upsets the whole system. With everybody closing the valves on a not so cold day the "heat cycle" is achieved quicker thus turning the boiler off sooner. Without a "constant" manual adjustments will have to be made to the Heat Timer throughout the whole winter.
If the handy man had a brain he would replace the air vents with something smaller thus slowing the steam entering a overheated room.
The other thing: think of radiators as digital not analog. It's not really possible to use the valve like a volume knob. It's either on or it;s off.

Boiler is sized for X amount of radiators. Turning off by valve throws off balance in system. Traps water in radiator leads to banging, hammering, leaking joints and other problems.

Steam Valves are rated by floor ie 1 goes on first floor, 2 second etc. The size of release hole is different.

Gets too hot, open top of window a few inches to let heat escape from ceiling. Need cooler still, then open bottom of window few inches to draw in cool air.[/code]

I might add: It is not the Tenant's responsibility to adjust their living style to suit the LL's heating system. If Vlad refuses to put the air vent in then you are stuck with opening and closing the valve. If you wanted to be a jerk about it you could find the right spot of the valve that would lead to a lot of banging. that would probably force the issue.

I suspect the boiler is excessively large for the building. It is overwhelming the float style air vents causing them to possibly clog in the open position. they could remedy this with smaller nozzles on the burner or checking if the high/low switch is low (of course). Turning the oil/gas feed to the boiler slightly off is also a quick fix. In the mean time replacing your air vents with the following would prevent the water.
http://www.bellgossett.com/WhatsNew/prd30Sep02.htm
This is that little vent in the picture above that is primarily used in hot water systems but also in steam. I use them all the time. It works better than the traditional float styles. They are adjustable.
It is not your fault! It's Vlad the lazy's fault.
My virtual tip jar below.

vanilla wrote: since you seem to know about these things, modsquad..... one day 2 of the 3 radiators in our apartment started leaking water from the air vent (model 40 style from photo) like a running sink. this was after a week of the boiler being WAY too hot. what happened to cause this leak do you suppose? the handy man said it was our fault for having the radiator off in the bedroom; but, this seems silly to me especially because one of the leaking radiator valves had not been closed. granted, i know not how these things work.

First, make sure the radiator has a slight pitch towards the valve. This will ensure that there is no water sitting in the radiator. If you have a level you can check to make sure it is angled slightly towards the valve. If it's not, try to lift up the end not attached to the pipe and put something under the legs, a small piece of wood or even some pennies. This will ensure that the water drains out of the radiator.

As modsquad said as well, the vent may be stuck in the open position which will also cause the room to get hotter than it should because steam will leave the radiator and enter the room. This should never happen, once the steam hits the vent it is supposed to shut off. You can get a new vent and change it yourself if the super won't do it. You really just need to unscrew the old one and screw in the new one. Just be sure to do this when the heat is off.

If you want to get really fancy you can get a thermostatic radiator vent which automatically stops letting steam into the radiator when the temperature in the room reaches a level that you set. They cost a bit but may solve your overheating problem if the other fixes don't.