In article .com, wrote:

I'll need to find out more about circulators before I can answer the
questions about those. Like what's a circulator?

It's a pump that moves the hot water around through the pipes.
Here's a pic of the ones in my basement:
http://www.milmac.com/Circulators.jpg

But the boiler does ignite and warm up, and water 'seems' to start
circulating in the apartment pipes.

If the circulator has failed, you'll get some small amount of circulation just
due to convection -- but not nearly enough. That might be the problem.

If the circulator is running, you should be able to hear it if you're standing
right next to it. They don't make much noise, but it should be audible. And if
you put your hand on it, you'll definitely feel slight vibration. If it's
working.

Electrical supplies to any motor load usually have a fuse in-line somewhere.
If the circulator isn't running, the problem may be as simple as a blown fuse.

You can learn a *lot* about how hydronic (hot water) heating systems work at
http://www.heatinghelp.com

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.