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.

How to test a microwave high voltage diode with a multimeter.

1. Unplug your microwave before beginning this inspection.
2. Locate and remove your high voltage diode to test it for continuity. To access it, you will first need to remove the cabinet and discharge the high voltage capacitor.
3. Set your multimeter to Rx1 and touch the probes to the terminals. Next, reverse the probes to check for continuity in the other direction. You should receive a reading that shows continuity in one direction, but not the other direction.
4. If your diode does not show continuity, or shows continuity in both directions, you will need a replacement high voltage diode.

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.

How to test a microwave door switch with a multimeter:

1. Disconnect your appliance from the power source.
2. Begin by verifying that the door hooks trigger the door switch mechanically. If they do, remove your microwave’s cabinet, locate your door switch, and remove it in order to test it for continuity.
3. Using a multimeter set to Rx1, while depressing the actuator button, touch the probes to the switch’s terminals. This test should produce a reading of 0, which indicates there is continuity.
4. If your test results do not match the results above, you will need a replacement door switch.

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.

How to test microwave magnetron with a multimeter:

1. Before beginning this inspection, verify that you have disconnected the appliance from the power source.
2. In order to access the magnetron, you will need to remove the appliance’s cabinet. Next, discharge the high voltage capacitor, then verify that the high voltage diode is working and that the mounting bolts are tight. Remove the magnetron to test it if no other issues are found.
3. Using a multimeter on Rx1, touch the probes to the terminals, this should produce a reading of two to three ohms of resistance. Next, move one probe to touch the metal housing of the magnetron. This test shouldn’t indicate that continuity is present.
4. If the results of your test do not match the results above, you will need a replacement magnetron.