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Kenmore Microwave Not Heating Up? Here’s Why And How to Fix It

The microwave is one of the most useful appliances you can own. While Kenmore microwaves are some of the most reliable on the market, breakages are bound to happen eventually. If your microwave runs but doesn’t heat, there are a few things you need to check out. 

Your Kenmore microwave might not be heating up due to several reasons. Three of the most common reasons why a microwave is not heating up are high voltage diodes, door switch, and magnetron. Replacing any of these parts is extremely dangerous and should only be done by a repair professional.

Even though professional help is required to fix most problems with your microwave, it doesn’t hurt to know what you are talking about when the repair person comes over. Maybe you are even learning how to be a technician! Read on to learn the steps involved in troubleshooting and fixing a microwave that won’t heat up. 

Kenmore Microwave Not Heating Up

Discharge the Capacitor

The first thing you need to do is unplug the microwave from the socket. To check the internal components, you will need to remove the microwave’s outer casing by taking out the mounting screws that run down each side of the machine, then unclipping the casing from the main body. 

That means you will need to discharge the high-voltage capacitor since this could carry a lethal charge even with the machine unplugged. 

I cannot stress enough how dangerous this step is. Do not attempt to discharge the capacitor at home. This should only be carried out by a professional. The capacitor is not always in the same place in different microwaves, so look up a guide for your particular model to locate it. 

  1. First, put on a pair of rubber gloves or rubberized work gloves for protection. 
  2. To discharge the capacitor, you will need a screwdriver or needle-nose pliers. You must be sure that the handle is made of rubber to insulate yourself from a deadly charge.
  3. If the terminal screws are exposed, you can lay a flat-head screwdriver across both terminals at the same time to discharge the capacitor. Make sure you are touching only the rubber, as touching the metal could kill you. 
  4. Hold the screwdriver’s metal against both terminal screws for at least 10 seconds to make sure the charge is gone. You may see a spark, but you may not.

Fixing the High-Voltage Diode

Okay, now that we have the dangerous business of discharging the capacitor out of the way, it should be safe to work on the microwave’s internal components. Of course, you should still wear rubberized work gloves to be safe. The most common reason a microwave would fail to heat up is if the high-voltage diode has burned out. Below are the steps you should follow to replace the diode. 

  1. The high-voltage diode will be attached to the high-voltage capacitor, which you have just discharged. If you are absolutely sure that the capacitor is no longer holding a charge, detach the capacitor’s diode. You should be able to do this simply by pulling it off the capacitor. You may need a pliers for this in order to protect your hands. 
  2. Next, unscrew the other end of the diode from the support bracket. 
  3. The diode may be visibly damaged, in which case it should be replaced. If you are not sure, you can test the diode with a multimeter. Set your multimeter to measure resistance (Ω) and touch the two terminals’ probes on the diode. 
  4. The diode should only allow current to run one direction. That means that when you test it, you should see infinite resistance when the probes are one way, and no resistance at all when the probes are reversed. 
  5. If the resistance is the same in both directions, then the high-voltage diode will need to be replaced. 

Here is a video showing you how to replace the diode:

Fixing the Door Switches

When you close your microwave door, the clips on the door slot into place, flipping switches that allow the microwave to start running. This system stops the microwave from turning on while the door is open. If they are broken, however, they may prevent the microwave from heating. Here is how to fix a broken door switch:

  1. First, you will need to remove the metal strip located on the front of the microwave above the door. This can be done by removing the screws on the front of the machine.
  2. Next, remove the control panel with the function buttons on it. When that is open, locate the switches. They will be on the side of the control panel where the door closes.
  3. Test the switches individually with a multimeter set to measure resistance. When the door is open, they should have infinite resistance. When it is closed, the resistance should be close to zero. 
  4. If the switch is too loose and the clip is not pressing it down, your solution may be to tighten the screws of the switch with a screwdriver. If the switch is being pressed, but the resistance is infinite, you will need to replace it. 

Here is a video showing you how to fix the door switches:

Fixing the Magnetron

The magnetron is the part of the machine that generates the microwaves, which are used for cooking your food. If your magnetron is broken, that may cause your microwave to blow a fuse, in which case the entire machine won’t work.

If the fuse doesn’t blow, the microwave will usually function normally but will not heat the food. Only an experienced professional technician should replace the magnetron. Here is how it is done:

  1. Remove the casing of the microwave to reveal the internal components. You should already have done this to discharge the capacitor and check the diode. 
  2. Locate the magnetron. It is a fairly large box which should sit close to the center of the microwave. Unplug the cable from the socket on the bottom of the box.
  3. Test the continuity of the magnetron by touching the probe leads of your multimeter against the two terminals. If the magnetron is working, you should get a reading of close to 0 ohms. If the resistance is infinite, then you will need to replace the magnetron.
  4. There should not be continuity between the terminals and the casing of the magnetron. This can also be tested with a multimeter. If there is continuity between the magnetron and the case, the magnetron will need to be replaced. 
  5. The magnetron will be held in place with 5 or 6 screws. When you have removed them, you should slide the magnetron out of the machine and replace it. 

You can type your microwave model number into the search bar above this page for a Kenmore 12664F Microwave Magnetron to find out which replacement you need. 

Kenmore 12664F Microwave Magnetron Genuine Original Equipment Manufacturer (OEM) Part

Here is a video showing you how to replace the magnetron:


Unless you have a significant amount of experience fixing microwaves, you should not attempt to change any of your machine’s internal components. The charge carried by the capacitor can be fatal even when the microwave is unplugged. Always call a professional technician. 

This article has shown you the steps involved in troubleshooting and fixing the most common problems that could be preventing your microwave from heating. 

Thanks for reading. Good luck getting your microwave fixed.


  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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