I can't give you a definitive answer but any loose connection will create a lot of heat which is clearly the case here. It may be that cleaning up the wire and connection and re tightening everything REALLY tight is all that is needed. Then again if the shower has seen some service it may be that it's nearing the end of its useful life. I don't think it will be to do with cold weather / inlet water temperature.
Richard
January 2009
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