Steam radiator will not heat up.

It also will not hiss. Does this mean that the vent is clogged? How do you remove and replace the vent? Can I do it myself? I am pretty handy.

It probably means your steam is turned off.

There might be air (or water, I can’t remember) in the system. Is the steam valve on one side at the bottom open so steam can get into the radiator? When was the last time you bled the radiator? Have you flushed the nasty water out of the system lately? Is the whistle clogged? You can get a new one for a few bucks.

Are you sure it’s a steam boiler vs. a hot water boiler?

The vent is screwed into a threaded hole of the radiator. After shutting down the boiler, you should be able to safely remove the vent and clean or replace it. Beyond that, has anything been done to the radiator since it last worked? Simple things, like upsetting the level of a radiator will adversely effect single-pipe steam. To learn more, buy a copy of “The Lost Art of Steam Heating” by Dan Holohan. Taught me much. Good luck.