The pressure washer will most likely remove only the paint that is already loose. As slickshif stated water/media blast would work but it's definitely not a DIY process. I've had good luck removing paint from old brick walls using Peel Away it did a good job and only left a few small areas that needed to be detailed by hand.
you'll have quite a mess on your hands thats for sure.
there are some other posts around here about chemical stripping.
I was able to get paint off concrete with a pressure washer from a local tool rental store. Depending on the nozzle you can do quite a bit of damage to different materials. Next time I think about needing one, I wont hesitate to get one of those gas powered guys. They are very quick, you will know right away if its working and you can pressure wash a house in just a couple hours.