Diagnosis
The microwave operates but does not produce heat. This is typically due to a failed magnetron or a defective high voltage diode.
How to Fix It
Unplug the microwave. Access internal components by removing the outer case. Test the magnetron and high voltage diode with a multimeter. Replace any faulty component. Reassemble and test.
If That Didn't Work
Verify the door interlock switches are engaging properly. A misaligned door can prevent the high voltage circuit from activating.
Heads Up
The high voltage capacitor can store a lethal charge even when unplugged. Discharge it safely before handling internal parts.