I have been having problems with my height controller sticking in the down position. I have replaced the linear motion bearings and rails, the band seal and rollers. After doing this it ran good for about a day and begun sticking again.
Best bet is to contact Hypertherm tech service....they are free, very easy to work with, and they spend all of their days helping people with Hyperthem products.
800-643-9878 Tel - Toll Free in USA