Rabbiofberlin: I just started reading this thread and I think your last posts very “enlightening” and if were submitted earlier, Oomis would have been spared a lot of grief.
Rav Moshe’s shita: Modern ranges, as you said, produces a flame because gas is constantly fed to the burner, like someone throwing logs into a fire from a pile. If someone were to hold this person’s hand, preventing further throwing of the logs, the fire would go out. So too, held Rav Moshe with gas ranges: when the knob is turned to lower the gas or to turn it off completely, it is NOT “kibui” but rather withholding the fuel (logs) from burning. So it has nothing directly to do with cooking per se. Therefore, holds Rav Moshe, lowering or tuning off the flame on Yom Tov is permissible.
Those who argue, say that the source of the fuel and the cut-off knob is too close to the fire and the burner reaction is too quick for Rav Moshes’s s’vara to be valid.
Regarding electric ranges, raising and lowering can only be accomplished with a single coil burner. Many electric ranges have a double coil and adjusting the heat for cooking purposes would not be permitted.
If these items were already mentioned, I apologize.