Our fireplace is about 7 years old and for the past couple of years, only the last opening in the burner has worked. I see the pipe's threading shortly where it comes out of the wall in the firepit, but when I try to turn the pipe with a wrench, the whole pipe, including the pipe the burner is connected to, turns. Any advice on replacing this pipe? And where I could even purchase a burner like this? Thought I would ask here before calling a chimney sweep.