Damage Boiling LEGO Bricks
The boiling temperature of water is 212 Fahrenheit (100 Celsius). The melting point of ABS plastic (the material LEGO is made of) is 176 Fahrenheit (80 Celsius). Therefore LEGO should NEVER be put in water that reaches boiling point or anywhere close to it. 

If you want to clean your LEGO, the best way is to just put it in a tub with luke-warm water and a mild soap. Let is soak overnight, then rinse it off with clean water. Here are some further references you can use:

http://thebrickblogger.com/2010/12/cleaning-dirty-lego/ and
http://thebrickblogger.com/2010/12/cleaning-dusty-lego/