Check the condition of the electrical contacts on the burner elements to see if there are signs of burning and pitting on them. If you find any, you need to replace both the elements and the ceramic plugs they fit into. If they are in good condition, you'll need to replace the control switches. Please post back to me, if you need parts information.
If my answer helps you, please click on the 'accept' button. That's how we experts are paid for our efforts.