Thank you for your question and I understand your concern.
Based on your symptom I would suspect the left front burner infinite is faulty and will need to be replaced.
left front infinite switch #9759474
can be ordered from Sears Parts Direct.
In order to access and replace the infinite switch, the cook top will need to un-installed to access the screws below the glass top. All the screws must be removed from the main top frame and then the top can be lifted off. Be sure to remove the knobs before lifting the glass top off.
NOTE: Disconnect the power supply by flipping the 2 house circuit breakers off before servicing.
I hope this is helpful. If I may be of further assistance as more details become available, please reply to this post.
If you do not feel confident repairing this problem yourself, then you can have it repaired at your home by a Sears technician. Here is a link for the website:
Sears Home Services