I don't know much about those, but are you putting it on the floor when you try to change the height? Sometimes, if you just turn the knob with with the wheels up in the air, it will look like the height isn't adjusted, but if it's resting on the floor, it will work, it needs pressure or something.... cheap eurekas with the knobs are like that.... Of course there could be a problem with that one or maybe it's not installed right, but most of the time, that has been my experience...