I recently purchased a Raypak 401a and I noticed that it does one metal bang after about 10 minutes after firing up and another one lesser one a few minutes after it shuts off. I had the installers come and take a look at it and they say that's normal for this heater as this is the metal expanding and contracting and that it will go away with time. is this normal? There are no codes and the heaters runs perfectly.
