By Rabbi Chaim Hillel Raskin – Rov of Anash in Petach Tikvah

In contrast to Shabbos, when lighting a fire is a melacha de’oraisa, lighting a fire on yom tov is not a melacha, provided it serves some yom tov purpose.¹ However, the chachomim prohibited lighting a new fire, since bringing the flame into existence (molid) resembles a melacha, and since one could light a flame before yom tov, it may not be done on yom tov.²

Since the prohibition of lighting a new flame is miderabanan, there is room to be lenient, in times of need, to ask a non-Jew³ or to ignite it indirectly.⁴ For example, if a mechanical timer wasn’t set correctly, and a crockpot or light is set to turn on too late, one could move the pin to turn it on earlier, since this is a delayed, indirect ignition.⁵ Similarly, one may gradually add cold water to an electric urn, even if this will later cause the heating element to ignite.⁶

Direct extinguishing is only allowed on yom tov for bona fide cooking purposes; otherwise, it would be an issur d’oraisa (see also issue 533).⁷

Indirect extinguishing, such as adjusting a timer to turn off earlier, is the subject of debate. While the Rama and Taz seem to be more lenient on yom tov that on Shabbos,⁸ the Alter Rebbe holds that on both Shabbos and yom tov, it is only allowed in a case of great need, monetary loss, or mitzva purpose. Thus, adjusting a mechanical timer to make a light turn off earlier would only be allowed for one of these reasons.

The Alter Rebbe notes that on yom tov, one may cause a candle to finish burning faster — extinguishing — by increasing the fire. Thus, one may add wicks to an oil lamp or lean a burning wax candle on its side so that the wax will melt faster. These are allowed since the goal is achieved by having the flame burn more powerfully. However, cutting the candle is forbidden because this causes it to finish faster by a means other than increasing the flame.⁹

See Sources (open PDF)

From The Weekly Farbrengen by Merkaz Anash