A heated seat should comfortably last as long as the rest of the car, so the fact that you have experienced two failures in this time period suggests there is a problem that has not been resolved. We would suggest going back to the dealer and asking them to repair the fault, although we suspect this may no longer be covered under warranty. If you would prefer not to pay the dealer for this work, you could consider taking the car to an independent Volvo specialist who would likely charge less than the dealer for a repair. You can find one near you using the Honest John Good Garage Guide here: good-garage-guide.honestjohn.co.uk/