
Microwaves have one job—heating your food quickly and efficiently. If your microwave does everything but heating, you might think it’s useless! However, if your microwave is still turning on, rotating, and lighting up, there can still be hope for repair. Read on to find out the most common causes of this issue, and how to fix it.
Safety note
Microwave repair has some unique safety challenges you must be aware of before you begin. Unlike many other appliances, microwaves come with a danger of electric shock even when completely unplugged. This is due to the high voltage capacitor, which can store enough electrical charge to cause serious shock and even death. It is possible to discharge the capacitor before working with the microwave’s internal components, but this requires specialized tools and knowledge and should not be attempted without the help of a professional.
Microwaves also emit potentially harmful radiation. Under normal operation, the radiation is contained in the outer shell of the microwave. If the microwave exterior is damaged, however, potentially dangerous radiation can leak out.
How does microwave heating work?
Before we get into the potential causes of a microwave not heating, let’s take a look at how the heating system in a microwave works. Unlike a regular oven, microwaves use electromagnetic waves to generate heat. These waves vibrate the water molecules inside your food, allowing rapid and efficient heating. Here’s how the process works:
- The magnetron generates high-frequency microwaves.
- The microwaves are guided into the interior cooking chamber of the microwave by the “waveguide.”
- The microwaves cause the molecules in the food to vibrate, generating heat and cooking the food.
- Water molecules are targeted most by microwave radiation, so foods with a high water content will heat faster.
Common causes of heating issues
A few different components work together to cause your microwave to heat up, and a fault with any of them can lead to issues. These include:
Magnetron problems
If the magnetron isn’t working properly, your microwave will have no way to generate electromagnetic waves. In this case, your microwave might appear to run normally, but no head will be produced.
Diode defects
The magnetron requires the diode to be functional to produce waves. The diode converts AC power to DC power. If it’s faulty, your microwave will not heat but may still appear to run normally.
Capacitor failure
The high-voltage capacitor stores the electricity that powers the magnetron after being converted by the diode. If the capacitor is faulty, you may notice heating issues, but there may also be visible sparking while the microwave is running. If you notice this, stop using your microwave immediately, as it could prove dangerous.
Blown thermal fuse
Most appliances that use heat contain a thermal fuse to shut the appliance off in case of overheating. If your microwave gets too hot, the thermal fuse will blow, preventing the microwave from heating. If this is your issue, you probably noticed that your microwave suddenly stopped working. Blown thermal fuses must be replaced to allow your microwave to resume normal function.
Door switch failure
To avoid microwave radiation escaping, microwaves have door latches that prevent the device from running if the door isn’t properly closed. If there is a failure with the door switch, your microwave won’t be able to heat, even if it appears to be fully closed.
DIY solutions
Due to the potential dangers of an unqualified person working with a microwave’s interior, only a couple of DIY solutions are recommended. If your microwave is running but not heating, try the following:
Reset your microwave
Resetting any appliance is a great first step if you experience any faults or performance issues. Somethings faults can be caused by software issues or glitches, and these can be eliminated by simply resetting the microwave and turning it back on. Here’s what to do:
- Unplug your microwave from its power source or switch off the corresponding circuit breaker. Wait at least five minutes.
- Plug the microwave back in and run a test to see if the heating problem has been fixed.
Test and replace the door switch
As described above, a faulty door switch can prevent your microwave’s heating mechanism from activating. As the door switch is located far from the capacitor and other high-voltage parts of the appliance, it’s safe for an experienced DIYer to test and replace this part.
- First, disconnect the microwave from its power source.
- Access the door switch. You may need to consult your microwave manual for advice on locating the switch in your particular model.
- Use a multimeter to test if the switch is functional. A faulty switch will show no continuity.
- Purchase a replacement switch that is compatible with the make and model of your microwave.
- Remove the faulty switch, making sure to note all the wiring connections.
- Put the new, functional switch in its place.
- Put your microwave back together, restore power, and then run a test cycle to ensure the microwave is now running and heating as it should.
When to call a professional
If you have tried resetting the microwave and replacing the door switch without success, it is time to contact a professional. Any other issues are too risky to be attempted by someone without training and could lead to serious injury or death. If your microwave is on the older side (more than about eight years), you may prefer to purchase a replacement appliance instead, as most microwaves don’t last much longer than 8-10 years.

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