I started a new thread on this because the old one was getting too
long. You can get the background he

http://groups.google.com/group/alt.h...9 bad0ef69ac0

http://groups.google.com/group/alt.h...ef f338195ed1

Ok, the room that has the radiator pipes in the concrete slab has been
isolated and I put about 22 pounds of compressed air into it. After 4
or 5 days it had lost most of the pressure. In a day or so it will
probably be empty.
I assume then that there is a leak in that room unless there is some
other furnace phenomenon that would cause a system to not hold
compressed air. Since I don't see any water I assume it's in the
concrete pad.

BUT...

The furnace it still losing pressure. Since all the pipes are either
visible or within the walls if this wood and sheetrock
house, I would assume that if there were an additional leak that I
would see a wet wall, a puddle or water dripping from a ceiling. I
see no water.
Someone in a previous thread said it could be a bad expansion tank.
The expansion tank is brand new and was installed after this pressure
problem started. The auto feed valve is closed and has always been
so, even when the system was not losing pressure. I'm not sure what
to do next or what to check. I can isolate another loop but I'm
wondering if it's a leak at all in this part.
Does anyone have any ideas?

Thanks for all the help so far.