GE Profile slide in electric range

We were getting an error message of F3 after our oven had been on for a half hour or so - my husband has changed the temperature sensor, it worked fine for a couple of days. Now the F3 error message comes on and also, after I turn the oven off we get an F2 error message after about 15 min. to 30 min. The oven is 17 years old - has it come to the end of its life?