I have a 2nd. hand glass top, self cleaning convection stove,Model 968-69973-1 . The burners in the front are large and the back small, with a warmer in the middle. When the left front burner is turned on, the burner only lights up the outer burner rings and on the right it only lights up the inner burner rings. I am assuming that this is not normal, if not could you please advise me as to what I need to do to repair the problem, thank you. Reg Gaudet