we have an old hot water heating system with the basement and upstairs on the same loop. basement has 2 existing radiotors we never used. we added a baseboard unit to the line and turned the system back one. since then we have had spotty performance with two of the units (the baseboard unit and one of the radiators). we would bleed one and get it working, but then the other one would get stone cold. any ideas on how this might be?