Under what circumstances and for what purposes may one use an oven for cooking or warming food on Shabbat? Of course, it is forbidden to turn on an oven on Shabbat. But assuming an oven had been turned on before Shabbat, may one use it for cooking or warming food on Shabbat?
If one wishes to place food in the oven and leave it there to cook until Shabbat morning, such as people often do with Cholent, he may, provided that he either places the food in the oven completely raw just before Shabbat (Shulchan Aruch siman 254:1) , or sees to it that the food is at least half-cooked when Shabbat begins (Yabia Omer, Helek 6, siman 32, ot 2.) If at the onset of Shabbat the food is neither completely raw nor at least half-cooked, it may not be left in the oven for use on Shabbat.
When one removes food from the oven on Shabbat, he must ensure that the motor is running before opening the door. If the motor is off, opening the oven door could cause the temperature in the oven to drop and thereby cause the thermostat to activate the motor, and the person would then have turned on the motor, in violation of Shabbat (Menuhat Ahava, Helek 1, page 57.) After one removes the food, he may not return it to the oven on Shabbat, even if the food is fully cooked and the oven had been turned on before Shabbat.
Some people put food in the oven on Friday afternoon, and just before Shabbat turn off the oven but leave the food inside with the door shut so that it remains hot for the meal. This is entirely permissible, but one must recall that after taking the food out of the oven he may not return it on Shabbat.
