Your seat is heated by electricity supplied by the car’s battery. The most likely culprit for your seat heaters not working is some issue with your battery or its ability to move electricity to your seat.
If no other electrical components are having trouble, your battery probably is not to blame. Next, you’ll want to look at your electrical connectors—both those attached to the seat heater button and the ones attached to the seat itself. If any connectors are disconnected or corroded, this is likely your issue.