Does one need to tovel in a mikvah a sandwich maker? It will be water damaged.
The general approach of Poskim is to be stringent in this matter.
From experience with toveling electronic utensils that “may not be immersed in water,” toveling does no damage, provided the utensil is allowed to dry completely (must be placed in a warm place for over 24 hours) before use.
An alternative option is for you to take apart the sandwich maker and re-assemble it.
Authorities dispute the status of electrical appliances that are used while being plugged into the wall. According to some poskim, these appliances are considered as being “connected to the earth” by means of the electrical cord, and therefore do not require tevillah (see Teshuvos Vehanhagos 1:450; Bais Avi 1:114; Chelkes Yaakov, Yoreh De’ah 41).
However, many dispute this position, and rule that the connection of an electrical cord does not render an appliance “connected to the earth.” The appliance therefore requires tevillah (see Shevet HaLevi, Yoreh De’ah 2:57:3; Chai Ha’Levi 4:60:5, 5:66:12).
Some suggest that because the appliance will get ruined, there is no obligation of tevillah; however, this position is not generally accepted by poskim (see Iggros Moshe, Yoreh De’ah 1:57-58).
A possible option for rendering such appliances exempt from the obligation of tevillah is to have the appliance taken apart and re-assembled by a Jew. In this situation one would not be obligated to tovel the utensil since it is considered as if the Jew created a new utensil (see Chochmas Adam 73:13; Be’er Moshe 4:100; Tevilas Keilim 11:50; among others).
However, experience has shown that in spite of the warning on the label, immersing an appliance in water does not cause it damage, and therefore the appliance should be toveled, and then left to dry for a lengthy period of time until it is completely dry. A blow drier can also be used to speed up the drying process. See Be’er Moshe 4:100; Rivevos Ephraim 2:172:10, see 3:502.
Note that although this is the writer’s personal experience, there are no guarantees, and for a particularly expensive appliance it may be worth considering the above option of taking apart and re-assembling the appliance. Yet, this this might imply losing the warranty.
There is no need to immerse the cord and the plug, which are not parts of the utensil itself. Poskim dispute whether the part of the utensil where the cord connects with the utensil needs to be immersed; see Iggros Moshe (above); Minchas Yitzchak 2:72; Chelkas Yaakov 2:61; Tevilas Keilim p. 206. The general custom is to be stringent for this.