If your vehicle is showing heated seats turn on but do not get warm, here are the most likely causes and the parts you'll need to fix each one.
The delicate wire grid inside the seat cushion often breaks from kneeling on the seat or general wear and tear. The switch will light up, but the broken circuit prevents the element from producing heat.
Moving the seat back and forth can pinch, stretch, or disconnect the wiring harness underneath. This is also a common error after deep interior detailing or stereo installation.
The switch's indicator light may illuminate to show it is turned 'on', but the internal electrical contacts that actually send power to the heating element have failed.
Many vehicles use a low-amp fuse for the switch illumination and a separate high-amp fuse for the actual heating elements. If the high-amp fuse blows, the lights work but there is no heat.
The computer module that regulates power distribution to the seats may have failed or requires a software reset, preventing the high-current power from reaching the elements.