We have a high efficiency furnace that heats water which is
piped thru a concrete slab. This is a question about air in the
liquid and bleeding of the system.

There is one accumulator in the system. It hangs down from
the piping and I assume it has a bladder. This is what I don't
understand. Why is it below the piping? If air gets into the
system (which it has) it has nowhere to escape. It continues to
race around the loop causing noise in the pump and flow regulation
valves.

Shouldn't the system's accumulator be above the piping to allow air
to move into it and out of the normal liquid flow? And if the
accumulator is not designed to bleed, then shouldn't there be a
high point reservoir, with a bleed valve on the top?

Thanks