Using an Urn with a Measuring Gauge on Shabbos

May recent models of urns be used on Shabbos?

Many recent models of urns come with a gauge which indicates how much water is in the urn. Since it’s connected to the main chamber, its water level rises and falls accordingly; thus, whenever water is taken from the urn, some water leaves the gauge and reenters the main chamber of the urn. If the water in the gauge isn’t heated before Shabbos, then letting water out of the urn will cause cold water from the gauge to enter the main chamber and be heated up, which is a very serious problem of mevashel (the prohibition of cooking) on Shabbos. 

Fortunately, the water in the gauge of many models is heated when the water in the urn is boiled for the first time; it then gradually cools off and isn’t maintained at boiling point like the rest of the water. If the water in the gauge hasn’t cooled down completely and is still warm enough to be served as a warm drink, there is no problem with it being reheated when it reenters the main chamber of the urn. In many models, all that needs to be done initially is to let a bit of water out of the urn before Shabbos begins, or to tip the urn backwards; doing so causes all of the water to heat up before Shabbos. However, if the water in the gauge cools off completely over the course of Shabbos, it becomes a problem again. 

There are certain urns on the market that come with rabbinic approval for Shabbos use. Alternatively, one should use an urn without a water level indicator, or examine how the gauge in their urn operates to determine whether it’s permissible to use it on Shabbos. One can also seal the hole of between the water gauge and the main chamber of the urn with duct tape which will prevent the water in the gauge from entering the main chamber. #520?

https://halacha2go.com?number=520

Practical Halacha: One minute a day. By Horav Yosef Yeshaya Braun, shlita, Mara D'asra and member of the Badatz of Crown Heights.