cherry: thank you.
ROB: The Rambam does not say that covering the fire is gram kibuyi, although he does put it next to the halachos of gram kibuyi. There is no Lechem Mishna on this Rambam, so I’m not sure what you are referring to. It’s true that Tosafos only mentions removing oil from the container, not cutting off the flow into the container. However we have yet to see that there is any distinction in Halacha. So we have a certain kibuyi according to Rashi and the Rosh, and probably also according to Tosafos. Turning off the gas line would probably have an immediate effect on the flame, but its not really the issue under discussion. The issue of boneh with electricity is a fascinating and often misunderstood topic, but not relevant to the issue at hand.