Seat heater elements
can be repaired if you're lucky.
I've done it twice to my driver's seat now. (two independent breaks) The element tends to separate in the base of the seat, not the backrest, as it's the base that gets the most punishment. It's a bit scary to remove the leather, but it doesn't have to wholly come off. The seat has two elements....one in the base and one in the backrest....they're wired in series, so when one fails, you lose the lot.
There
is a little thermostat in there too and it's fitted at the rear of the seat base just under the leather (at the back where the leather disappears down under the backrest) You can feel for it under the leather.
As long as the indicator light in your heater switch comes on when you press it, then it's receiving power ok from the engine running relay. If you can put a multimeter on the pins of the brown connector in the pic above (NOT the airbag one!!!) you should read about 2.5 ohms for a cold element. Infinity means you have an open circuit....ie, time to peel the leather back.....
A link to seat heater repair
here (you have to be registered though) and also shows that thermostat.