Next thing to do is to check the piping for any sags or dips which might be holding water -- that can block steam or air (so you need to check the returns, too) and usually also causes a water hammer -- but not always.MichaelJohnston said:I just had two steam traps replaced but that didn't fix the issue where these two particular sections of radiator are not heating up. The contractor suggests cutting the pipe to flush the runs. What do you do when you live somewhere where no one knows how to deal with your system?