10 reasons for your microwave sparking – why it happens and what you can do about it

Written by David Lewis
6 Min read
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Why is my microwave sparking and crackling

Seeing a microwave sparking from the inside whilst trying to cook or heat up something can be extremely worrying, but there is actually a multitude of reasons this could be happening. We’ve identified 10 of those reasons here:

Did you know that the microwave was invented by accident?

In 1945 a self-taught engineer was testing a new vacuum tube called a magnetron when he discovered a chocolate bar in his pocket had melted from the heat. He tested the tube again by placing popcorn kernels near the magnetron and was shocked when they popped into life. By 1947 microwave ovens were available to buy.

Today, more than 90% of all U.S. households own a microwave oven and there is a multitude of different styles, makes, models, and sizes available. But with the average microwave estimated to last around seven years with normal use (much less with heavy use) the list of faults and problems that can occur is relatively lengthy, one of the most common being an oven that sparks when it runs.

microwave sparking

Metal inside the microwave

In the huge majority of cases, sparks inside the appliance when switched on are most likely because a small scrap of metal has been left somewhere – a tiny sliver of foil left on the cooking dish or a metal spoon accidentally still inside a mug.

These sparks are caused by a build-up of charged particles which produce a concentrated electric field at the edge of an object, for example along the tines of a fork.

To resolve this issue, switch your appliance off and remove the plug before thoroughly examining the contents for any evidence of metals – whilst the sparks won’t harm you or start a fire, they could permanently damage your microwave, leaving you with a hefty bill.


Even after your oven is switched off and disconnected from the power socket, there is an extremely high voltage stored in the large capacitor, which can give you a very bad shock and has been known to be fatal. If you are at all unsure, leave it to a professional.

Damaged wave guide cover

The wave guard cover is situated inside your oven and helps to distribute the waves to make sure the food is cooked evenly. They also prevent food particles or bugs from entering the magnetron.

During the cooking process, small amounts of oil, grease, or food particles might escape from the food and stick to the wave guard cover where the heat from the magnetron will burn and ‘spark’, consequently damaging the wave guard cover.

A damaged wave guard cover will cause frequent sparks every time you use the oven and will need to be replaced as quickly as possible.  

Damaged rack support

If your oven features a hook-like part, then this is your rack support. Sometimes, the support can become loose or the paint on the rack can wear out, when either of these things happens the result will be your microwave sparking during the cooking process. The rack support will need to be replaced as soon as possible if you notice sparks from this area of the oven.

Diode burning

Diodes are essential elements of your oven, used for generating, mixing, detecting, and switching signals. Faulty diodes might emit a burning smell, crack in two, or display a crack or a blistered spot – any of these issues could cause a spark and should be investigated as quickly as possible.

Incompatible cookware

If you’re using utensils or cooking dishes that aren’t labelled as microwave safe, any sparks in your oven might be related to these.

Cookware is deemed to be microwave safe if it falls into these categories:

  • Won’t heat up directly because there’s no water in it
  • Won’t melt when food hits it indirectly
  • Won’t leech chemicals into your food when it’s heated
  • Doesn’t contain metal

Faulty stirrer

The stirrer helps to ensure there is an even distribution of heat inside your oven. If the stirrer is malfunctioning for any reason and the heat and energy is collecting in one area of your oven this can lead to burning and sparking.

The microwave needs cleaning

A heavy build-up of dirt and grime on the inside of your oven can cause sparking which is often accompanied by a burning smell.

You should give your microwave a clean once a week to keep it working at its optimum level. If you heat a lot of messy foods like sauces or gravy you may need to clean it more often.

Combine baking soda and water in a heatproof bowl and heat it for around three minutes, allowing it to sit for a couple more minutes before removing and wiping around the inside of your appliance.

Failing magnetron

The most common reason for a faulty magnetron is that it has overheated due to deflected microwave energy, which can sometimes be caused by running the microwave when it’s empty.

If your microwave is making an unusually loud humming noise, popping or clicking as well as sparking, then your magnetron may need some attention.

Turntable lug

If you happen to notice that the sparks are coming from the bottom of the microwave, specifically from underneath the turntable plate, then you may need to replace the turntable lug.

The turntable lug is a plastic coupler that sits between the turntable plate and the motor, allowing the motor to rotate the plate.  If this lug cracks or is damaged, the metal spoke will be introducing metal into the microwave.

Convection rack or crisping pan touching walls

Some microwaves come with a removable metal rack that has been specifically designed to fit that make and model. The rack gives you more space to be able to heat up a couple of dishes at a time and attach to plastic or rubber clips. If these plastic or rubber clips come loose, the metal rack will directly touch the other metal inside the microwave and cause sparking.

Always remove the rack unless you need the additional cooking space, and only use racks that have been specifically designed for use in your microwave model.

In summary

Sparking microwaves can cause panic, but in most cases, they’re not dangerous.

You’ll need to unplug your appliance and investigate the cause of the sparks, but the risk of the sparks causing a fire or damaging your health is extremely low. However, sparks inside of your microwave could cause damage to the oven and should always be taken seriously. If you’re unsure it is always best to call in a certified professional for advice.


Can I use my microwave after it sparks?

In most cases, sparks inside a microwave are caused by metal that has been accidentally left inside – a small amount of foil over a cooking dish or a tiny thread of wire wool after cleaning. In these instances, once the offending metal has been removed you are safe to use the microwave again.
However, if your microwave continues to spark when you use it, you should remove it from the power source and arrange for a certified professional to investigate the cause of the sparks – it could be due to a damaged electrical element which will need to be replaced before you can use it again.

What are the signs my microwave is going bad?

Microwaves don’t last forever, and at best you’ll have seven or eight years of use from one. Some of the tell-tale signs that it’s time to invest in a new microwave oven include:
·       It’s unusually noisy
·       You can smell burning when you use it
·       It won’t switch on or respond when you push buttons
·       The door handle is malfunctioning
·       The turn table has stopped rotating
·       It doesn’t get hot

Can a microwave explode?

Just like conventional ovens, a microwave could catch fire or explode if it has faulty wiring or is misused in any way. Certain foods like grapes, mugs of water, and whole eggs can trigger fires due to their shape and structure.

Can a microwave burn you?

Microwave radiation has the potential to burn you, just in the same way it can burn food. There are two areas of the body that are particularly susceptible to this – the eyes and the testes because of the lack of blood flow in these areas to be able to carry away excess heat.

Appliances made simple. 

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