I have a Tappan Millennia stove. The two front burners are not working right. They are difficult to start and don't reach full flame anymore. The low and high settings are basically the same and there's no graduation of the flame as I turn the dial. The power burner won't even boil water. The two back burners are working fine. These don't seem to be typical burners that I've run across before. Other stoves I've been able to lift the top to access all piping/ductwork and burners.