DIY Repair & Maintenance

Solved! Why Is My Microwave Not Heating?

If your microwave is not heating like it should, try these troubleshooting tips to decide whether it needs repair or replacement.
Microwave Not Heating


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Q: I’ve tried warming my leftovers and heating my tea in the microwave without success. Is my microwave not heating because it’s broken and can’t be fixed, or is there a way to repair it?

A: It’s an inconvenience to lose the ability to reheat food and drinks in mere minutes. Microwaves are a bit of a mystery to most of us, so it’s natural to assume that they’ll require replacement the moment they stop working. If your microwave isn’t heating, a number of parts can be responsible for the issue, from door switches to magnetrons. With the help of a multimeter, you can troubleshoot the three most common problems on your own; just be sure to unplug the microwave before inspecting the inner workings! However, if you’re unsure of how to approach the problem, it’s perhaps best to utilize the services of a professional to help diagnose and fix the issue.

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If a microwave doesn’t heat, there might be a problem with the high-voltage diode.

Microwave Not Heating and the High Voltage Diode Problem

The diode is the piece of equipment that helps channel and provide the electricity in one direction to the magnetron, and it’s usually located behind the microwave front panel near the controls. If it’s burned out, then the microwave won’t generate power to spin the magnetron and heat the food.

You can remove the front cabinet panel using a Phillips-head screwdriver (after first unplugging the microwave) and check the polarity of the diode using one of the best multimeters. It should show low resistance in one direction and high resistance in the other. If not, or if it shows continuity on both ends, then the high-voltage diode needs to be replaced. Sometimes the diode shows correct polarity, and in this case, a qualified technician may need to check the overall high-voltage power circuits in the microwave.

It might be a problem with the door switch: A microwave won’t heat until the door is in a closed position.

Occasionally, the door switch on an older microwave can fail to lock properly, especially when the door is slammed frequently. It’s a good safety mechanism, as a microwave would be operating unsafely with the door open. A good indicator that the door switch is the problem is if the light stays on when the door is shut and the microwave isn’t running.

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You can check for this issue by unplugging the unit, unthreading the exterior screws and removing the outer cabinet housing, and using a multimeter to check whether there is any power coming through the switches. If your microwave has a button to release the door, press it down while checking the door switches. If the terminals of the microwave read zero, they have continuity. If not, the switches will need to be replaced.

Microwave Not Heating and the Magnetron Problem

The problem may be the magnetron, which generates the heat for the microwave.

When a magnetron fails, it can also blow fuses, which can cause other failures in the microwave. You can check to see if the magnetron is working by unplugging the unit, removing the cabinet housing, safely discharging the high-voltage capacitor, and removing the magnetron. With your multimeter, you can check the charge from the terminals. They should read 2 to 3 ohms of resistance if the magnetron is still working. Then, use one probe to touch the metal housing that encloses the magnetron; if it reads zero, there’s a problem. This step should only be completed once the capacitor has been discharged properly using a rubber-handled screwdriver or other safety tool.

It’s recommended that a professional replace a faulty magnetron due to the dangerous nature of high-voltage repairs. You can also leave the diagnostics of the magnetron to a professional if you prefer. Depending on how old your microwave is, it’s worth considering replacing the unit completely if the magnetron has gone out.

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Make sure the timer is not set to cook several hours in advance.

As embarrassing as it is, microwaves occasionally fail to operate due to our own user error. It’s a good possibility that many of us have rarely used the extra feature buttons on our microwaves, as we usually just need a couple of minutes to pop a bag of popcorn or sterilize a cutting board. If your microwave is not heating, you might want to check to see if the delay timer was set to begin cooking at a later time. You can always unplug the microwave for a moment to reset the system if the timer doesn’t cancel easily.

Make sure you are not heating items that cannot be microwaved.

Microwaves are handy for reheating leftovers, warming water, and much more, but believe it or not, they are not able to heat up certain foods. Though the instances of making this error are uncommon, it’s a good idea to check that you’re not heating up very dry or fat-free foods. While the physics behind the phenomenon are more complex, microwaves essentially heat up the water and fat molecules in food better than they heat up other molecules. So, if your food isn’t heating fast enough or it isn’t heating at all, it may be because the food is fat-free, very dry, or both. Remember that there are certain foods and materials that should never be heated in the microwave for safety reasons. Heating metals can cause significant damage to your appliance (and even your home), and defrosting meat in the microwave can be unsafe due to bacteria growth.