kenmore 790.92603013 if the burners are on, oven won't heat

kenmore 790.92603013 if the burners are on, oven won't heat I have an old kenmore stove model #790.92603013 Occasionally if the burners are on, the oven won't heat... if I already have the oven on though, the burners work just fine. Broil always works. What does that mean?