Hi. Check out the following thread.
Looks like it applies to S80s as well!!
http://www.volvoclub.org.uk/dc/dcboa...id=2402&page=3
It is a known problem about seat heaters and fires/short circuits.
Some people (cannot remember which forum I have read it on) have had to jump out of their cars as their seats caught fire!!!!
I say take it to a dealer pronto!!!
Dan.