BSD
Pashuteh Yid & PM: Fourth Chelek in Orech Chaim (forget exactly where) R. Moshe deals with this issue of Drabannan vs. Deoraysa for melacha Shetl”g. I think he says most Rishonim argue on the Magen Avraham who holds Kiboyi is worse than starting a new flame, and therefore holds one should light anew rather than lowering; Rav Moshe argues and allows lowering of a flame for cooking purposes.
The “Chiddush” is from Orach Chaim first Chelek, but he says he does not want it to be printed, but its along the lines of a gas cutoff is stopping additional fuel, not removing it (Ayin Shom).