How do you know you have heat damage?
I think I have heat damage because the very front of my hair is loosely curled(even though I used/and the salons used heat protectant on my hair) I only used heat to blend my extensions, not the rest. At first, my hair was very straight, but after a few washes/and co washes my hair became curly again. My hair still shrinks, but not as much as the rest.
It is probably heat damaged, but not as severely as could be since it curls back up. Heat protectant, while helpful, definitely isn't a fail-proof way of protecting your hair.
Sounds like heat damage to me. If you said the ONE section you regularly flat iron doesn't curl up like it used to or like the rest, it's probably heat damage. Even with the best heat protectants, you can't use heat that often and expect 100% no damage. Check out this article: http://www.naturallycurly.com/curlreading/home/how-can-i-get-my-curly-hair-back/