I have a brand new microwave. The first thing that I cooked was some uncovered chicken. Does this make the microwave only fleish or can I boil a cup of water to return it to parve status?
Yes you can, but it should not be done on a regular basis. Although it is the minhag not to kasher a pot from meat to dairy etc. it is permitted to kasher it from meat or dairy to pareve. The way to kasher it, is to make sure the inside of the microwave is clean. Then place a cup of water in the microwave for a nice long cycle until the inside of the microwave is full of steam. Then in order to kasher the part of the tray that was under the cup, move the cup to a different part of the tray and repeat.
Darcei Teshuva Y:D 121-59, Shut Maharshal 2- 241, Livushei Mordechai 3 -212, Maadanei Osher 160-7, Kashrus in the Kitchen pg.212, Horav Osher Wiess and Horav Y. Berkowitz.shlit”a, (R’ O. Weiss says that the microwave should be heated for 30 minutes).