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Kosher Nexus
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“Kashering” a Dishwasher for Pesach – by Rabbi Re’eim Hacohen, Rosh Yeshiva and Chief Rabbi, Otniel

Question: How can a dishwasher be made kosher for Pesach?

Answer: The first thing that is necessary is to understand how a dishwasher works. The typical dishwasher has two baskets where the dirty dishes are placed. At the bottom of the machine, there is a hole where the water is collected. A heating element heats the water to various temperatures as required by the different washing programs. The water does not boil, and typical temperature is about 60 degrees. At the bottom of the dishwasher is a pump that sends the water through a filter, where the remains of the food are separated from the water. The filtered water is fed to sprinklers at the bottoms of the baskets that hold the dishes, and this spray of water is what cleans them.

Hot Water

The general rule in making something kosher is that “the way that something is absorbed is the same way that it is discharged.” According to the Mishna, “If one takes a dish from an idol worshipper: What is commonly immersed should be immersed, what is put in boiling water should be boiled, and what is made to glow from heat should be heated to the glowing point.” [Avoda Zara 5:12]. Rashi explains, “Boiling water – such as pots made of metal, which should be cleaned with boiling water.” It would thus seem that since the dishwasher absorbs the chametz from hot water, it can be made kosher for Pesach by cleaning it and running the hottest program in the machine.

Is Boiling Water Necessary?

The question of whether the process can be performed without any need to bring the water to a boil should be discussed further. Terumat Hadeshen (150) quotes from Sefer Mitzvot Katan that water must be boiled and not just heated. In the Shulchan Aruch, the RAMA writes, “Purifying with water – hag’ala – does not do any good if the water is not boiling” [452]. However, this seems to refer to a case where the original food was absorbed in contact with boiling water, but if the water did not boil (as in a dishwasher) perhaps it is sufficient for the water to be merely hot. This is explicitly written in Terumat Hadeshen, who quotes from the Mordechai that dishes which absorbed food from hot water can be made kosher using water that is hot but not boiling. This is also the opinion of the author of the Shulchan Aruch (451:5). The great recent masters agree with this opinion too. Examples are Pri Megadim (Orach Chaim 323:1, 14) and Mishna Berura (452:8).

In Igrot Moshe, it is suggested that a hot stone or piece of metal should be placed in the water at the bottom of the dishwasher, so that boiling water will be used (Orach Chaim 58). The author bases his ruling on the RAMA, but in my humble opinion this should not be done because at the bottom of the dishwasher is a filter made from plastic which might melt, so that the equipment might be damaged. The RAMA proposed using a stone because in principle for Pesach use he does not consider the way a vessel is most often used. The fact that usually the water does not come to a boil is therefore usually not relevant in the opinion of the RAMA, but in a dishwasher the water never reaches the boiling point at all, so a hot stone is not needed for them.

Must the Baskets for the Dishes be Replaced?

I have heard some rulings that require replacing the baskets which hold the dishes in the dishwasher. This is based on several responsa by the author of Igrot Moshe, who fears that some of the original food will remain and can then touch the dishes in the machine. But Igrot Moshe requires that the baskets be changed in the case of using the machine for both meat and milk, not for Pesach. This is because before Pesach the equipment is thoroughly cleaned and there is no fear that actual food particles remain on the baskets. In addition, in my humble opinion for modern dishwashers this entire possibility is relevant only with respect to the silverware holder, such that even for switching between milk and meat it is sufficient to thoroughly clean the silverware holders. There is no need to replace the baskets, since this would be quite expensive, and “the Almighty does not waste the money of Yisrael.”

Rinsing after the Dishwasher has been Kashered

Based on the responsa of Rashi, the Shulchan Aruch rules that the dishes should be rinsed with cold water immediately after they have been kashered. It would seem that there is no practical way to rinse the dishes in this way. There are several replies to this point. First, the rabbis have ruled that if the rinsing step is omitted, the dish is still kosher. In addition, it is possible to follow immediately after the koshering step with a washing program that begins with a flow of cold water, thereby acting in accordance with Rashi’s demands.


The dishwasher should be cleaned thoroughly, especially the filter and the sprinklers (by dismantling them). It is recommended to add a scale-removing substance to the water (instead of the usual detergent), and then the dishwasher should be turned on being left to idle for a period of twenty-four hours. The washing program that gives the severest conditions should be used. One who wants to be especially stringent can follow this with a second program that starts with a flow of cold water.

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