Question: Is one permitted to use an electric hot water urn controlled by a Shabbos clock to boil water on Shabbat?
Answer: We find numerous views on this matter.
A Jewish soldier once asked the gaon Rabbi Menashe Klein (Responsa Mishneh Halachot 4:34) about placing raw food before Shabbat on a stove controlled by an electric timer. The timer would turn the stove on sometime on Shabbat and would cook the food for when he needed it.
Rav Klein notes that the gaon Rabbi Yisrael Weltz, av beit din of Budapest, Hungary, and later of Jerusalem, discussed a related question (Responsa Halachot Ketanot 1:189). Since we have a rule that there is no shevut bamikdash – no cessation of work in the Temple – why couldn’t the goat sacrifice of Yom Kippur be cooked in the following manner: Light the end of a long rope that leads to a pile of wood and place the raw meat of the sacrifice in a basket hanging over the pile of wood; as night falls, the fire on the rope will reach the wood under the sacrifice and ignite it?
Rav Weltz underscores this question with a citation from Responsa Mata DiYerushalayim (Tractate Mo’ed, Jerusalem Talmud). The author if this work heard from his rebbe, the Chatam Sofer, that the Jews in Frankfurt, Germany, would brew coffee on Shabbat by putting small pieces of wood in a pile on Friday and under that pile place a rope with a mixture of slow-burning sulfur. The far end of the rope would be lit. The lit part of the rope would flicker all night until the morning by which time the fire would reach the wood, which would ignite (Yalkut HaGershuni 255).
Both these cases seem to involve mechanisms similar to our modern Shabbos timers.
The gaon Rav Klein also notes that the Maharam Schick (Responsa, Orach Chayyim 157) and others permit setting a timer on the eve of Shabbat for the purpose of turning on a light on Shabbat. The Maharam Schick notes that even though some prohibit it, “everyone is lenient in this regard today.”
Returning to the question of cooked food, Rav Klein goes into a lengthy discussion and cites many sources – mostly from the era before electric cooking or timer-controlled gas ovens – that would permit setting a timer to cook food.
Yet, he concludes by stressing that his permission is only for the particular soldier who wrote to him about his particular situation, which is a she’at ha’dechak (an emergency-like situation). He writes that since electricity is a relatively new halachic topic, he won’t extend his permission to any other case. Thus, from Rav Klein we have no proof that setting a timer to begin cooking food on Shabbat is permitted.
The gaon Rav Moshe Stern, who writes extensively about modern-day Shabbat questions relating to electricity (Responsa Ba’er Moshe Vol. 6 Kuntres Electric, part 1) was asked: “Is one allowed to put a full pot of water on an electric hotplate which is not yet turned on but will go on with a timer, such as a Shabbos clock, in the morning and then will boil the water? If this is permitted, would it also be permitted to cook food [in the same manner]?”
Rav Stern responded that only boiling water is permitted, and one must cover the control knob with tape (or remove the knob entirely). He adds that even the plug should be taped as a heker, a sign, that it is not to be touched.
Rav Stern also cites the same Mata DiYerushalayim on the Yerushalmi, noting the custom in Frankfurt. He writes that an electric hotplate is even better than an open flame of firewood whose coals a person might stoke.
Rav Stern, citing the Rema, the Taz, and the Magen Avraham (Orach Chayim 253), also states that the water pot must be placed on the hotplate before Shabbat. Placing it on Shabbat itself is forbidden.
He also limits his permission to boiling liquids such as water, tea, or coffee. It remains strictly forbidden according to Rav Stern to place a pot of raw meat and the like before Shabbat on a hotplate that will turn on due to a timer sometime on Shabbat morning.
The gaon Rav Moshe Feinstein doesn’t even permit boiling water with a Shabbos timer. He reasons that if we permit this activity, we essentially permit all kinds of other activities that are prohibited on Shabbat, especially in factories, and there can be no greater denigration of Shabbat (zilzul Shabbat).
He writes that had electricity and Shabbos timers come out in the era of the Tanna’im and Amora’im, they would surely have forbidden using them just as they forbade amira le’akum, telling a gentile on Shabbat to perform labor on one’s behalf. He adds that setting a timer to go off on Shabbat to cook a food is not the same as placing raw piece meat on a burning stove just before Shabbat. In the latter case, the action started before Shabbat.
As for timers for electric lights: Using them is based on an old custom of gentiles extinguishing gas lamps. In some places, gentiles even lit lamps on Yom Kippur for Ne’ilah. Although some opposed this practice, since so many were lenient in this regard, we do use timers for electric lights.
Rav Feinstein concludes, though, that using timers for cooking and other prohibited labors is forbidden.