My driver's seat heater has a mind of its own. It turns on whenever it feels like it, sometimes non stop. Sometimes it does, sometimes it doesn't. It always works when I want it to. It can be a pain shutting it off 30 times in 30 minutes.

 

It’s more than likely the driver door module. Not the seat heater switch.

 

the door rubbers like to leak water in that corner. pop off the heater switch carefully open it and clean it up many times they get corrosion from water intrusion.

 

x2 caused by moisture intrusion. "Sometimes it does, sometimes it doesn't" (only acts up when raining or car wash?)
clean and seal the contacts. Also, inspect/check for the leaking seal/weatherstrip . In the meantime, you can disconnect the green connector under the seat.

 

Again here is a YT video on the DDM.