- Megavolt

Taken from: ERETZ HEMDAH

Question: May I set up a dishwasher on a timer, so that I will load it on Friday night with the night’s dishes and it will go on overnight? Can I do the same thing in the afternoon so that by the time Shabbat is over, the afternoon’s dishes will have been done?

Answer: At first glance, there would not seem to be fundamental problems with operating the machine on a timer, as the same activation of the electric device and the heating of the water will occur regardless of if you fill the racks with dishes. As for the removal of the grime from the plates by using hot water (which occurs only because you put the plates in), that is not considered borer (removing impurities) or bishul (cooking). The reasons this is true are beyond our present scope. Some say that the soap is being cooked and should be put in before Shabbat (Techumin XI, pp. 137-154).
However, a safety device usually changes everything. In order that hot water should not come out of the dishwasher, the system is designed so that the machine works only when the door is locked until the end of the cycle. Obviously, the door is open when you load the dishwasher on Shabbat, and then you must lock it in order that the timer will be able to activate the machine. Closing the door thus causes the prohibition of Shabbat to occur at a later point when the timer will activate the dishwasher. Such a delayed reaction is only gerama, which is not a full violation of Shabbat, and is permitted in certain special situations that warrant a low-level violation of Shabbat (see Shabbat 120b and Rama, Orach Chayim 334:22). However, in most cases, it is forbidden to cause such a delayed reaction. For example, we do not allow one to press the buttons of an air conditioner to make it go on when a timer activates the system.
There is a technical solution, albeit a problematic one, that one can arrange with an electrician’s help. You can by-pass the aforementioned safety device (The Zomet Institute provides this service). Then when you lock the door, it will make no difference regarding the dishwasher’s operation. Unless one can ensure that this will not cause dangerous situations (such as opening the door during operation), we would say this is forbidden because “danger is more severe than prohibitions.” However, we cannot preclude the possibility that someone can create safeguards.
Regarding using the dishwasher a second time, when the dishes will not be reused, there is an additional problem. It is forbidden to prepare on Shabbat for after Shabbat (hachana), even if the preparation does not include a prohibited action. Filling the racks with dishes need not be preparation, as many people find it a good place to temporarily store dirty dishes. However, refilling detergent is clearly done to facilitate cleaning the dishes, and if they will be used only after Shabbat, it is hachana.
A final issue, which may or may not cause it to be forbidden to have the dishwasher go on, is called avsha milta. The Rama (Orach Chayim 252:5, as opposed to the Shulchan Aruch, ad loc.) forbids operating from before Shabbat a mechanism that is forbidden to operate on Shabbat if it makes noise. This problem certainly exists if the system went on by timer during Shabbat. It is permitted only if it is common for people to set up the mechanism in advance and thus there is no reason to suspect that one desecrated Shabbat in its regard (ibid, regarding a chiming clock). This could be a problem for a dishwasher. Rav Moshe Feinstein (Igrot Moshe, OC IV, 70) says that the forbidden level of noise is such that it is expected to be heard in the next room, which is borderline for a dishwasher. While Rav O. Yosef (Yechaveh Da’at III, 18) and Rav N. Rabinowitz (Si’ach Nachum OC 15) say that avsha milta applies to dishwashers, regarding relatively quiet models, this issue would not be a problem.
In short, while there may be a way to use dishwashers on a timer on Shabbat, a combination of technical and halachic problems makes it not simple in practice.