Typically, what you see is yours to maintain, including the radiator, the radiator valves and radiator vents. The pipes aren't leaking, the valves are, and are subject to wear and tear just as your toilet flush valve and faucet washers are. The coop is not responsible for repairs to your apartment, however, it usually is responsible for your entrance door, the bottom lock and the exterior windows.
If the super is willing to replace the valves for the cost of parts and his labor, it's probably cheaper than having a handyman or plumber come in. He can also coordinate the shutdown of the boiler while he does the work.
Maintenance covers the staff salaries, building insurance, common area repairs and maintenance, building mortgage, heat, hot water, etc., but not repairs to individual apartments, unless damage is caused by a leaky pipe within the walls or ceilings, or damage from rain leaks, etc.
The occupant of the unit above you is liable for damages to your apartment if their radiator leaks or their toilet overflows.

Thank you!

While the apartmeant envelope idea is helpful there are subtleties.

Unlike some of the other plumbing, the radiators might be considered part of the building equipment and the responsibility of the corporation rather than the lessee. Our Proprietary Lease (from the mid-80s) is written that way.

If your radiator is not original building equipment and was replaced by a former lessee, then it could well be your responsibility.

Also, in NYC generally the valves have to be either fully open or fully closed or else they leak. This is a common cause of damage to the apartment below. But it sounds like you have had the super inspect and spoken with management already, so maybe not your situation.

We've struggled with who is responsible when a component is trans-envelope, like radiator pipes, shower and bath P-traps, waste lines, etc. If both the board and affected shareholder are reasonable things are usually worked out.

Regarding the problem of fully open or closed radiator valves, we've installed Danfoss valves on most radiators. They replace the traditional screw valve. In their basic form they are like the OEM screw valves, but intended for continuously variable settings. Their main benefit is that a fully mechanical (no electrical connection required) thermostatic unit can be fitted to the valve which provides fairly granular temperature control by regulating the amount of steam or hot water entering the radiator. I highly recommend them.

This is your condos responsibility, contact your super and tell him or her your radiator is leaking. This is part of your HOA Fees

Hi Anon -- Firstly, please realize that almost *everything* you read here is someone's opinion. The questions you are asking fall under the general realm of "legal" and since I am not a lawyer the opinions I am about to express are worth pretty much what you're paying for them.

That being said, you should start by reading your Proprietary Lease. Most PL's for co-ops formed in the 1980's and after used a standard template. There should be sections in your PL that delineate which areas in your building are "common" and the responsibility of the co-op corporation, and which are proprietary to individual shareholders. Read those sections carefully because the wording is sometimes confusing.

1) In my building, we interpret shareholder responsibility to be anything that is within the envelope of the unit (i.e. four outer walls, ceiling, and floor) to be the responsibility of the shareholder. Anything outside of the envelope is common area. The PL carves out a few specific exceptions, but for the most part this is how we decide. One of the reasons for this is the co-op has very little control over the quality of changes or updates made by a shareholer to their unit. If a radiator was replaced and the contractor used sub-standard parts and shoddy workmanship, the co-op cannot automatically assume financial responsibility for their repair or replacement.

2) The cost of the work will come out of your pocket. Unless stated otherwise in the PL or House Rules you are not required to use the building's super to make the repairs. You should be able to bring in a licensed and insured plumber from the outside. Check with the board for any rules they may have about this. You will need to coordinate with the super because at some point the steam or hot water will need to be turned off to your apartment line while the repairs are underway. If there are no definite rules about using the super, to keep from ruffeling feathers, you might ask him/her for a cost estimate and then get competative bids. That way your decision will appear to be a purely financial one.

Check with the insurance company that carries your co-op owner's policy to see if any part of this is covered and if it is worthwhile for you to file a claim.

Finally, ask the attorney who handled your purchasing of your unit. He/she should have read your proprietary lease and may be able to give you more than the opinions I've provided above.

Good luck!