cold rads -- sometimes ???

i have a hot water boiler w/ circ pump.

from the boiler, supply to rads branches off in three directions. 2 of the 3 (loops) always get hot (on 2 floors). the 3rd loop (two floors) only warms up when some of the other rads are turned off

is this a balancing problem ?? or is it possible there is an air lock in the line of the third loop ??

thanks for any assistance. -- cooper

try balancing cant do any harm as long as you remember what was set where before you started