My bike did the same and was out of warranty.

There isn't really anything wrong with the rectifier, it's the multi pin connections that are sh*t. If you take the connections apart you will probably see some burnt plastic where one of the pins has had a bad connection. I didn't replace anything, just wired a better connection on the one pin that was obviously at fault on my bike. Sealed it up with a piece of old bicycle inner tube and a bit of insulating tape. Still going strong 4000miles later.