601. A Pot on a Stovetop

Shabbos 3:4

If food has not been cooked sufficiently to be served, if water has not been brought to a boil, or if food has been cooked sufficiently to be served but further cooking will improve the taste, it may not be left on the fire on Shabbos even if it was placed there before Shabbos. This is a preventive measure lest one rake the coals in order to speed up the cooking process or to cause the food to cook more thoroughly. Therefore, one may leave food on the heat if he removed the coals before Shabbos or covered them with ash, etc. In this way, it is clear that a person has distanced himself from cooking the food and there is no danger that he will rake the coals.

Shabbos 3:5

The above applies to a stove that is not that hot. In the case of an oven, however, even if one removed or covered the coals, food may not be left in it, on it, or even near it. That refers to food that was not completely cooked or that was completely cooked but will benefit from further cooking. Since an oven is very hot, a person does not distance himself from the cooking. Therefore, the possibility remains that he will stoke the fire even if it is only straw or stubble, or if it is covered.