How to Fix a Microwave That Won't Heat

Your microwave may turn on but not heat up. This could be caused by a problem with the high voltage diode, which helps to power the magnetron. The high voltage diode is located in the cabinet. Unplug the microwave and discharge the high voltage capacitor after removing the cabinet. Test the diode for continuity using a multi-meter; there should be low resistance in one direction and high resistance in the other in a working diode. If the resistance is low in both directions or has no continuity, the diode needs to be replaced. If the diode tests normally, the issue may be with the high voltage circuit, which should only be tested or replaced by a qualified technician.

When your microwave turns on but does not heat up, it may mean the door switch is broken. The door switch signals other microwave components to supply power when closed, and to stop heating when open. The door switch can also be called an interlock switch. When this part doesn’t work, the fan and stirrer motors may still function, which makes your microwave look like it is working. You can access the door switch by removing the cabinet; first unplug the microwave. The door switch usually has wires marked C for common, and NO for normally open. Use a multi-meter to check the switches while depressing the actuator button. If there is no continuity at that point, replace the switch. During your test, ensure that the door hooks which trigger the door switch are working properly, as that could also cause this issue.

A microwave that does not heat up may have a broken magnetron. This is the part that makes the heat to cook the food. If it is broken, it may blow a fuse in your microwave which could lead to other components failing. Before testing the magnetron, you will need to unplug the microwave, remove the cabinet, and discharge the high voltage capacitor to protect yourself from an electrical shock. Test the magnetron by disconnecting its attached wires and attaching the leads of a multi-meter to the magnetron terminals. The continuity should show two to three ohms of resistance between the terminals. The magnetron will need to be replaced if it shows no continuity, or shows continuity between the terminals and the grounded outer case of the magnetron. If your test with the multi-meter comes back normal, then further testing might need to be done by a certified technician.