Originally Posted by Dockhead
I haven't heard of a failure on that. It's a pretty simple device (thermistor I think).
If you are considering getting a lot of spares it's probably better to look for a used working unit on Ebay and just keep it as the one spare. On our boat it's faster to change a whole unit than an individual part. There are usually a couple available all the time.
Also, it's a good idea to burn a couple liters of kerosene (or Jet A) once or twice a season. Just feed the little clacking pump from a small jug.