Which is a correct English cook on low fire or low flame or low heat?

Answer 1

Which of these expressions you might use depends on what kind of heat you are cooking on. "Low flame" is something you would say if you have a gas stove, and "low heat" suggests an electric one. I have not heard "low fire" but it might be used by people who cook on open fires (a rare thing these days).

Answer 2

A low heat would be most appropriate.

Answer 3

In North America, you could say either "low heat", or "low flame". You would never say "low fire."