Microwave Sparking: What It Means, and How To Fix It

Microwave Sparking

Stuck trying to figure out why your microwave is sparking?

Don’t worry, I’ve been there too. There’s nothing quite as alarming as trying to reheat leftovers in the microwave and seeing sparks instead.

Luckily, you can quickly fix some microwaving sparking problems yourself.

If your microwave is sparking, turn it off immediately and inspect the interior to identify the cause of the issue. There’s a good chance you accidentally left metal or grapes inside, the waveguide cover is broken, or it has a faulty diode.

Read on to learn how to solve the problem!

4 Reasons Your Microwave Might Be Sparking

Unlike traditional ovens, which work through convection, microwave ovens heat food through electromagnetic waves which are known as microwaves.

Most of the time, these are perfectly safe. However, in certain situations, these electromagnetic waves can turn into electricity. That’s when you start to see sparks in the microwave.

Microwave Diagram Appliance Analysts
Microwaves work by using high-frequency electromagnetic waves to heat your food. These waves can turn into electricity when they interact with conductive materials.

Luckily, there are only a few reasons why that would happen. Most of them are relatively easy to fix, too.

#1 Metal in the Microwave

Never put metal in the microwave! You’ve probably heard that before, but you may not know why. Well, metal and electromagnetic waves don’t get along well.

When metal goes into the microwave, it creates sparks – lots of them. The electromagnetic waves get turned back into electricity, causing a serious light show.

If your microwave is sparking when it runs, the most likely reason is that there’s metal inside. You may have left your spoon in your coffee or some tin foil on your leftovers. Even a small scrap of steel wool left after cleaning can lead to sparking.

Note: If your microwave is sparking after cleaning, please avoid using steel wool. Instead, opt for soft cloths or sponges.

#2 Broken Waveguide Cover

But if your microwave is sparking without metal, you might want to keep reading.

When the unit makes the microwaves that cook your food, it projects them through a little panel known as a waveguide. When the waveguide cover is broken, your microwave is in trouble.

The waveguide cover is in place to protect the electronics in the microwave oven. With a broken waveguide cover, steam and even food particles can build up in the electronics.

If you notice sparking coming from a panel in your microwave, a broken waveguide cover is probably the cause.

#3 Faulty Diode

Faulty diodes are the least likely reason that your microwave is sparking, but they’re also the worst.

Your microwave use diodes to create waves and cook your food. If you have one or more faulty diodes, you’ll start to see sparks. Your microwave will probably stop working shortly afterwards, too.

#4 Grapes

Yes, grapes can cause your microwave to spark! However, if that’s the cause, you probably did it on purpose.

Cutting a grape nearly in half and then microwaving it can cause plasma and balls of light to form in your microwave.

This can damage your microwave, of course, so don’t try it with a unit you want to use in the future.

How to Fix a Sparking Microwave: 4 Simple Steps

To fix a sparking microwave, you need to figure out the problem first. Here are four steps to stopping a sparking microwave, every time.

  1. Turn off the microwave immediately. If the sparks were extremely bright or seemed to come from the walls of the microwave, unplug it to turn it off. You don’t want to risk electrocution!
  2. Check to see whether you put any metal in the microwave. If you left cutlery inside or used a metal dish or tin foil, that was probably the cause. Remove it and you should be all set.
  3. If there’s no metal in the microwave, check the waveguide cover. That will be a small panel on the inside of the thicker side of the microwave. If it looks cracked or damaged, that’s probably the cause of the sparks. You’ll need to order a replacement waveguide, then unplug your microwave and replace it. With some cheap microwaves, it’s simpler to just get a new unit. More expensive models might be worth saving, though.
  4. Finally, if there’s no metal and the waveguide looks fine, it’s probably a faulty diode. In that case, leave the microwave unplugged and call a professional repair person. Otherwise, just get a new microwave and recycle the old one.

What Materials Cause Sparking

The easiest way to keep your microwave from sparking is to make sure you only use microwave-safe materials. Certain substances are guaranteed to cause sparks, so it’s best to avoid them.

  • Metal forks: Thin metal tines are guaranteed to cause arcing electricity and sparks. Spoons aren’t much better. Keep cutlery out of your microwave.
  • Tin foil: The foil you wrap your food in is a great way to accidentally cause microwave sparks. The metal reflects the electromagnetic waves pretty much perfectly. Unwrap your food before you microwave it.
  • Steel wool: You get sparks with steel wool for the same reason forks and tin foil cause it. Even worse, steel wool can be flammable, so you’ll have bigger problems. Clean your microwave with something else.
  • Poptart wrappers: The foil wrapping on breakfast instant pastries can act a lot like tin foil in the microwave. Take the wrapper off before you heat your breakfast.
  • Grapes: The small size and high water content of grapes leads to a special hot-spot reaction. If you cut a grape almost in half, but leave it connected, the two halves will start to create plasma between the two of them. It’s a fun experiment if you don’t need your microwave anymore.

Is a Sparking Microwave Dangerous?

In most cases, you’re perfectly safe if your microwave starts sparking. However, if you see sparks in the microwave, you should still turn it off immediately.

Sparks will damage the inside of your microwave permanently. So, while sparking microwaves aren’t dangerous to you, they are dangerous to themselves.

There is one situation when a sparking microwave is dangerous. If it’s sparking because of broken electronics, then the microwave might pose a risk of electrocution.

If you’re not sure whether the microwave is safe or not, just unplug it. That will help you avoid any dangers and investigate the problem more closely.


A sparking microwave can be scary. Luckily, it’s usually not dangerous.

Unplugging your microwave and removing metal from the inside will help stop most sparks in their tracks. If it looks like there’s a faulty electrical component, your best bet is to call in the experts. That will keep you safe and keep your microwave from sparking in the future.

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Thanks for reading, and have a great day!

Hi there! I’m Craig, and I’m the founder of Appliance Analysts. When it comes to appliances and anything electrical, I’ve always loved opening things up, figuring out how they work, and fixing them. This website is where I share free advice from myself and our experts to help our readers solve their appliance/HVAC problems and save money. Read more