Bob Lang wrote:
To replace a broken valve on one my radiators, I've drained the water
from the hot water heating system in my house. Now I don't know how to
refill it! Can anyone help?

Replying to my own post here, and thanks to Ed for your reply. In
case anyone has a similar system -- it seems that there are many
different types -- here's what you do: The boiler does indeed
have an automatic filling mechanism, but it may not just start on
its own once you empty the system of water. The expansion tank on
the boiler has a schrader valve on it (like the valve on your
car's tires). Take a bike pump and pump it up to about 12psi.
This is what starts the automatic filling system. You'll hear the
water start to flow. It may take a few hours, depending on how
empty the system is. I haven't turned the heat on to bleed the
system yet, but my impression is that the pressurized expansion
tank somehow helps regulate air pressure inside the system,
reducing the need for bleeding. We'll see :-)

-Bob