Sorry, I'm having a hard time remembering (June). I went through that too-needed a new heating sensor and I had to pry the whole plaque off and send it, as they sent a whole new box, minus the door, racks, wood tube, etc. Of course they tried a new temp control first (not the problem) so I DID have to look up the warranty number, could have sworn that was where it was.
I will look when I get off work, unless Ron or someone can answer you first.
I looked again-there are 2 plaques-bottom one in Spanish. In the bottom LEFT corner of the upper plaque it says serial number. In the bottom RIGHT corner is a number under the 800 phone number. I belive this is the serial number. Mine is 07080017. Hope this is correct. When you get on the phone with them they will tell you what number and where it is if in doubt. Hope this helps.