It should be checked for safety once a year. The internals are exposed to moisture from the chimney and you want to get the safety control checked. My concern would be the quality of your oil. If it is several years old it can possibly start to degrade. In large hospitals where they store diesel underground for backup generators they run a bunch of it out and replace it with fresh oil once a year or have additives added to keep it up to snuff. I would talk to your oil company about that. Gasoline loses its octane after a year. Our pro Beenthere may know more about this.