On Thu, 3 Mar 2005 08:34:06 -0600, (m Ransley)
wrote:

I bleed my radiators when it is running from each radiator. You have a
pressure gauge on your boiler you should rely on as autofill valves are
not always perfect. Also filling should be done on a cold boiler not
hot. If you bleed with the unit off and cold nothing may happen , or
little compared to when it is hot and under higher pressure. I have
found my autofill to over fill by 3lb.


It sounds like the original poster is talking about a hot water
circulating system as opposed to the steam heating system that you
appear to be discussing. Although there are similarities, hot water
and steam system heating are different. For one thing, most hot
water circulating radiators are not furnished with air blead valves.
They have two connections (and input and an output for the circulating
hot water- Steam radiators generally have one pipe connection to the
steam supply - the water condenses down the the same pipe) The hot
water system designer is supposed to supply a blead valve at the
highest point in the the system. Automatic air blead valves are also
available.

The incoming feed water, to a varying degree will have disolved gases
in it (mostly air, which is about 78% Nitrogen). The air can impede
the flow of hot water to certain parts of the system and thus, the
radiators will be cold if it is not removed.

If you've got a lot of air in the pipes, there is nothing wrong with
bleeding it while the system is off (circulating pumps, not working).
However, to truly purge the most possible air out of the system, you
have to do it when the pumps are running. Presumably, you have an
auto-fill valve somewhere to supply fresh water to make up for any
lost volume. There should also be an expansion tank somewhere on the
system to keep the pressure uniform as the hot water expands.

Beachcomber