I have a question i m trying to get heat on the 3th floor and i cant now when i try to purge the water on the 3th floor barely no water comes out with the lower boiler vale close. when its open water comes out with ease. so i change the air vale on the line thinking maybe the line has air and it still the same. the psi is 8 to 10 pounds so could it be the pressure or do i need to change the circulator pump. the pump about 8 or more years old. the 1st and 2nd floor is older but still working and i am getting heat on the 1st and 2nd floor not the 3th.