It is the microwave part that doesn't heat; we don't use the convection. We have already pulled out the unit. The model number is XXXXX; serial LF946282S. It is only less than 5 years old. It did this temporarily once before; then spontaneously went back to heating.
We have an appointment for GE to look at the microwave. Of course I am accepting your answer, I just want to be sure I can come back and discuss this with you if needed.
Thanks for your input!