On Nov 26, 7:54*am, bud-- wrote:
Vented?
Meaning there is a tank at or above the highest radiator and the tank
has an open top? If that is what you have the tank water level has to be
above the highest radiator.

The boiler has a vent/filler tube on top, with a rain cover. It
passes air freely.



Other wise there should be a tank that has an air cushion. As water and
the pipe expand at different rates the water has to have somewhere to
go. I goes into the tank and compresses the air. The other thing this
tank does is pressurize the system. The compressed air maintains the
pressure. If the tank doesn't have a diaphragm to separate the air and
water the air can dissolve into the water and the air cushion
disappears. Then you close the valve from the system to the tank and
drain the tank. This is similar to a well system. The open top tank does
the same thing.

Sorry, this type of system doesnt have that kind of thing.


If you don't have an open tank above the top radiator there should be a
pressure gauge. You fill the system to a pressure at least 1/2 psi for
each vertical foot from the gauge to the highest point in the system.


Nope, nope, nope.

If the water (not bleed) valve at the radiator is leaking it should
never let air in. The pressure should always be positive so water would
leak out.

You would think so.