Question:
Would one be able to bring water to a boil in a utensil using a microwave, then insert an even meluban into the utensil to overflow the water in order to kasher the utensil?
Answer:
The Shulchan Aruch O:CH 452- 4 says that we can not do haga’la with water from chamei Teveria, because it isn’t heated by fire, because taste that was absorbed by heat of a fire can only be purged by the heat of a fire. The poskim say that the same would apply to a microwave, that we can only do hagala with the heat of a microwave if the vessel became trief with the heat of a microwave, but not to kasher taste absorbed with the heat of a fire.
As a side point, you question is not really too applicable, (for kashering glass) because we can not heat water in a metal utensil, as it will cause the microwave to go on fire, plastic is sceptical if it can be kashered in the first place, and pottery ceramics ca also not be kashered..
Sources:
Shvus Yitzchok 6-9 ( 18) in the name of R’ Eliyashiv zt”l, Kovetz Halachos 11-17, Ohel Yackov 452-5 (4) in the name of Knei Bosem and R’ M. Deutsch shlit”a, Also see Halachos of Pesach pg. 156. Also see Even Yisroel 9 pg. 102, and Halichos Shlomo 3 ftnt. 3 regarding water heated by solar heating.
