I'm having trouble adjusting the flame level on one of my burners. The flame is set too low on one of my burners so when you turn the knob all the way down to low, the flame goes out. I have removed the knob and tried to turn the small screw to adjust the flame level higher, but when I turn the screw nothing seems to happen one way or another. I have turned the screw around so many times, I'm not even sure where it was initially set. I was able to adjust the other burners using the same method without a problem. Am I doing something wrong on this one?