there seem to be a lot of problems with the handwarmers just suddenly not working anymore. Most of the time it is just a discontinuity (wire cut or shorting out) in one of the grips. If you have a multimeter you should be able to check resistances to see if there is continuity or not in the grips. Could also be a bad relay, bad rheostat, or the CDI. You dont want to just go buying a CDI suspecting that is the problem though, because they aren't cheap, and you can't return it, so if thats not the problem you are pretty much screwed out of that money.