Is the button illuminated or no?

 

With auto start, the seat button light comes on and goes off almost immediately. The only way to get it come on and work is to turn off the engine and turn it back on with the key. Steering wheel heater works just fine.

 

Almost sounds like an ambient temp issue, but then your steering wheel should turn off as well.

Look HERE
Post #16 on. Could be software related, especially since turning the truck off(resetting circuit) allows you to turn seat heater on.

Try unticking the radio box, remote start your truck and see if the switch turns on the seat heater and stays illuminated. If so, this will allow you to turn on when you get in without shutting of truck until the issue can be resolved.

 

Just noticed this thread and have to comment.
My 2010 turns on both the seat heating light and the steering wheel light when I use the remote start.
However, neither seems to get warm. This morning it was -14F, so outside temperature would surely justify the heaters coming on.
It's been this way since new although I rarely use the remote start being too cheap to waste the gas warming up the truck most days.