A GE microwave may not be heating because either the diode or magnetron tube has burnt out, one of the door switches is defective, the high voltage capacitor is defective or a fuse has blown out. Less common possibilities are that the thermoprotector or control board is defective.
The GE microwave's power diode is responsible for boosting the voltage of the appliance to allow it to properly cook the food. If the power diode burns out there is insufficient power to operate the magnetron, the component that is actually responsible for heating the inside of the microwave. Power diodes that malfunction are easy to recognize, as the are visibly burned. The diode burning out is the most common reason why a GE microwave does not heat up.
Another reason why a GE microwave may not heat is due to one of the magnetron's tubes burning out. This problem is also relatively easy to diagnose as the internal roof of the appliance is burned.
The door switches are a safety mechanism designed to prevent the microwave from turning on if the appliance's door is not closed completely. Most GE microwaves have three door switches. If one of the switches is defective, the appliance does not heat.
Owners should not attempt to repair a broken GE microwave, because certain components, such as the high voltage capacitor that is also responsible for heating the appliance, can retain a charge up to 3,000 volts even if defective.