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