I just bought a catalyst stove a few weeks ago. It is my first stove of this style. The stove was used and is 6 years old. I have noticed a lot of postings stating the Cats last 6-8 years. I think this one will last longer, because I can tell my the condition of the stove it was used sparingly over the last 6 years. My question is, when the Cat starts to go bad and goes bad, what are the symptoms? How will I know when it is going bad or gone bad?