Thee have been lots of posts in the past two years concerning overheating issues with the M55 insert and its over heating issues. Here is a photo of the problem. If you look at the shaft from the motor going in to the tangential fan you'll see it's crooked. The weight of the motor causes the motor itself to sag which slows down the RPM thus causing the issue. FYI this motor came out of a Vista Flame M55 FS. Really, any M55 stove with this motor will eventually garner this issue.