There's a temperature limit to the black knobs; I can't recall it off the top of my head.
I think 375 degrees. The silver knobs usually have to be purchased separately Minda. Who ever flamed out their knob probably had the oven temp too high even for preheating? Or it was a defective knob as you speculated.
You can remove the knobs and switch them out, they sell them separately.
My flame DO has a black knob but I don't put it in the oven... but now I'm curious LOL
Thanks everyone. Good to know. This may be a good reason to look for a Provence DO since it has the silver knob, lol