Operating a Dishwasher with a Shabbos Timer
Question
Is it permissible to operate a dishwasher with a Shabbos timer? We’ll set the timer on Friday, and on Shabbos night after the meal, the dishwasher will wash all the dishes that used for the meal for us?
Answer
It is forbidden. The reason is that it is forbidden that a device that may not be used on Shabbos operate on Shabbos in a way that can be heard. The reason is that it’s disrespectful of the Shabbos and it appears as if it was operated on the Shabbos itself. This is true for both the case where the device was turned on on Friday and did not finish its operation when the Shabbos began, and when it is operated on Shabbos by a Shabbos timer. However, in case of a great loss, one can rely on the lenient opinions.
Source
Remo (Orach Chayim, section 252, paragraph 5; Mishnah Berurah ibid.)