Unfortunately, I didn’t put bleeder valves on the high point of the baseboard, so I can’t bleed these. On the return side, right above the circulating pump, there is a valve that you can connect a hose to and just below the valve (on the same fitting) is about a 1/4″ diameter pin with a screwdriver slot in the end. If you rotate the pin, it apparently opens and closes the opening. Do you know what this fitting is for and what is the purpose of the pin? Can I possibly get the air out of the system this way? My expansion tank is on the supply side, if it makes any difference. I really appreciate your help. THANKS!