In my 2005 997s the heated seats work sometimes.
They turn on but shut down on their own, then turn back on.
Both seats are doing this at the same time, so if one stops so does the other one.
When the heated seats turn on the work fine for about 10 minutes or more.
I am thinking the control unit must be going bad, but it looks like it is connected to the a/c-heat controller.
Anyone have a problem like this?

 

Sounds like they may be "cycling" on and off, and perhaps that is normal? Especially if it's related to the HVAC thermostat setting.
That's just a guess, as I don't have much experience with that particular option here in AZ, even though my car has it.....

 

Mine is the same, they work for a few minutes and shut down. My Mercedes is the same. I believe this to be normal and intended to warm you up initially on a cold day till the car's HVAC system takes it from there.

 

Something is broken becuase some times both heated seats won't turn on, but other times they both work fine for a few minutes.

 

Was your battery disconnected or did the car sit for a long time recently? My car sat unused for a month in January and seat heaters stopped working, took it to Dealer and they reset them.