I have the above from new for over 10 years. Recently when turning the flame in the main oven up with the control knob the flame will either go up or go really low but it will not go to medium setting flame (gas 5 or 6), the top part of the actual oven is very hot but the bottom and middle is only warm, took over 3 hours to cook a small chicken today. please can someone advise.

Sammy, February 2014