I have a 4mth old SF3100. I developed 2 cracks at the top of door on each side. I was told to send pictures of my set up. Once received they saw that a manual damper was installed on my chimney. Thet said that these caused the stove to over heat, hence the cracks. However, in the manual it recommends that a manual damper be installed. I am a little confused. Would the manual damper cause this problem?