Incarnate Balrogs?

[onewhitetree]

Balrogs again, yes.

Balrogs were not known to change their forms (this leading into the infamous wings discussion which hopefully can be left alone), and so could be, by this assumption, incarnate Maiar, like the Istari. If they are incarnate, and thus have perishable bodies, how did the one in Moria survive for so long buried under the mountain? Surely it needed something to keep aflame.