Why Is My Microwave Sparking? (5 Common Reasons)

Categorized as Microwave Repair and Troubleshooting
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Opening your microwave door to find concerning sparks and flashes inside can be an alarming experience for any homeowner. However, there are several common issues that can cause microwaves to spark, most of which can be easily diagnosed and repaired.

In this comprehensive guide, we’ll explore the top 5 most common reasons for microwave sparking and how to troubleshoot each potential issue. With some basic microwave maintenance and replacement of worn parts, you can stop sparks before they become a fire hazard or ruin your microwave completely.

Here’s a quick answer: Microwaves commonly spark when metal objects like foil or utensils are accidentally placed inside. A damaged waveguide cover, worn turntable ring, built-up debris, failing magnetron, or faulty diode can also cause sparking. Inspect the interior for debris, test components, and replace worn parts to stop dangerous sparking. If sparks persist in an older unit, replacement may be necessary.

Overview of Microwave Sparking

First, let’s overview some microwave basics to understand what causes sparking in the first place.

Microwaves work by producing electromagnetic waves that cause water molecules in food to vibrate rapidly, creating heat energy that cooks the food. This is all powered by the magnetron, which is the main component that generates high-power microwave frequencies.

These electromagnetic waves are transported into the interior oven cavity through the waveguide, which is usually a small metal box or cover inside one wall of the unit.

Sparks can occur when microwaves encounter metal, which reflects the electromagnetic radiation instead of absorbing it like food does. This generates electrical arcing that appears like sparking.

While occasional small sparks may not cause immediate issues, consistent sparking can damage the inner oven over time or even become a fire risk if left unaddressed.

Now let’s look at the 5 most common culprits behind microwave sparking.

1. Damaged Waveguide Cover

The waveguide cover is one of the most prone areas for sparking since any damage, warping, or gaps in this panel can allow leaks of microwave energy into the cavity. Metal fragments, grease buildup, and general wear and tear over time can all damage the waveguide.

Signs of a faulty waveguide cover include:

  • Sparks coming from the general area of the waveguide
  • Poor cooking performance, uneven heating
  • Burning smells from the waveguide area
  • Visible damage like warping, cracks, or deterioration of the cover

Fix: Carefully inspect your microwave’s waveguide cover for any signs of damage. The cover is usually held in place by screws or tabs. Remove the cover and clean built-up grease deposits with isopropyl alcohol. If the cover is warped, cracked, or otherwise damaged, replace it with a new one specific to your microwave model. Make sure the new cover seals tightly with no gaps.

2. Worn Microwave Turntable Rings

The turntable ring at the bottom of the microwave chamber allows food to rotate for thorough, even cooking. However, these rings contain small metal parts that are usually coated in a protective plastic cover. Over years of heavy use, this plastic coating can wear off and expose the metal pieces underneath. This exposes metal to microwave energy, leading to sparking.

Signs of a worn turntable ring:

  • Sparks originating from the center or bottom of the microwave
  • The turntable makes grinding, scraping noises when rotating
  • You notice damage, chipping, or wearing of the plastic coating

Fix: Remove the turntable tray and ring and inspect the ring closely. Replace the ring if you see any metal exposure. Only use turntable parts specifically designed for your microwave model, as the dimensions are carefully designed to avoid sparking.

3. Metal Objects or Foil in the Microwave

One of the most preventable causes of microwave sparking is putting metal objects or aluminum foil inside the microwave chamber. Utensils, foil, plates with metallic paint or trim, twist ties, and other metal items can all lead to sparking and arcing when subjected to microwave energy.

This usually occurs due to someone unfamiliar with microwave safety placing these items inside, especially elderly family members or children.

Fix: Thoroughly check the microwave interior for any forgotten metallic objects like utensils, loose foil, or food packaging. Only use microwave-safe cookware and completely avoid foil. Supervise children using the microwave closely and educate family members on microwave safety.

4. Faulty Diode

Behind the scenes, microwaves rely on diodes to function properly. This electronic component helps regulate voltage delivered to the magnetron. If the high-voltage diode fails, it can disrupt energy flow in the microwave and cause sparking.

Signs of a faulty diode include:

  • Sparks and unusual noises from the microwave back/top where the diode is located
  • Uneven cooking or failure to heat food properly
  • The odor of burning plastic

Fix: You will need to test the diode with a multimeter to confirm failure before replacing it. However, extreme caution is required when working with the high voltage components in a microwave, making this a job best left to professional appliance repair technicians. The cost is typically $100-$150.

5. Failing Magnetron

The magnetron deserves special mention here, since problems with this crucial component can manifest as sparking in some instances. The magnetron converts electrical energy into microwave radiation to cook food. Over time, from long usage, this part can simply wear out and begin to fail.

In addition to sparking, signs of magnetron failure include:

  • Microwave power seems weak, food cooks slowly
  • Unusual humming or buzzing noises from the microwave
  • The odor of burned electronics

Fix: Again, extreme caution is urged here. A failing magnetron indicates your microwave is too old and unsafe to continue using. Professional installation of a new magnetron costs $200-$300 on average – likely more than a new microwave. Instead of repairing an aging unit, we recommend replacing your microwave once the magnetron shows signs of failure.

When to Replace a Sparking Microwave

While many causes of microwave sparking can be addressed with maintenance and repairs, consistent sparking in an aging unit or sparks originating from the magnetron are signs that microwave replacement provides the only long-term solution.

Here are signs your microwave is too old and unsafe to continue sparking:

  • Your microwave is over 10 years old
  • Sparking has persisted despite replacing parts
  • There are burn marks inside the unit from arcing
  • You smell burning or see smoke
  • The door does not seal properly anymore
  • Rust, outdated design features, or lack of safety advances make an aging microwave less safe in general

Rather than endangering your home and family by persisting with an outdated sparking microwave, replacement with a new unit is the wise choice.

Cost of Replacement vs Repair

The average lifespan of a microwave is 5-10 years. Once a unit reaches or exceeds that age, the costs of repairing an aging microwave often approach or exceed the cost of buying a new model:

  • New microwave cost: $40 – $150 for a basic 700-1200 watt model
  • Professional microwave repair costs:
    • Magnetron replacement: $200-$300
    • Diode replacement: $100-$150
    • Waveguide cover: $100+
    • Total repairs: $400 – $600

With affordable new microwave options under $100, replacement becomes the better investment compared to sinking funds into extensive repairs for an old unit.

Microwave Sparking Troubleshooting Checklist

Here is a checklist summarizing the steps to troubleshoot and address microwave sparking:

  • Inspect the interior for any metal objects like foil or utensils, removing anything found
  • Check for signs of a damaged waveguide cover, replace if needed
  • Remove and inspect the turntable ring, replacing if worn or damaged
  • If sparks persist, contact an appliance repair technician to evaluate the diode and magnetron
  • If the unit is over 10 years old, consider microwave replacement instead of sink repair costs into an outdated appliance
  • Always take proper safety precautions and never operate a known sparking/damaged microwave
  • Monitor the microwave closely anytime it is in use after repairs to ensure sparking does not return or worsen over time.

Following these steps can help you determine the root cause, resolve microwave sparking promptly, and take appropriate action if the unit needs retirement. With attention and care, your microwave can continue operating safely for years of reliable service.

Microwave Sparking FAQs

Here are answers to some frequently asked questions about sparks in microwaves:

Is it normal for my microwave to spark a little?

Small sparks can occasionally occur in normal operation. However, consistent or excessive sparking indicates a malfunction needing repair.

Are microwave sparks dangerous?

Consistent sparking can damage the interior cavity over time. More importantly, regular sparks can escalate into an electrical fire hazard. Have your unit inspected as soon as sparks are noticed.

Where do microwave sparks come from?

Sparks originate from microwaves encountering metal surfaces like damaged waveguides, turntables, foil, or utensils. Arcing occurs as electricity jumps between metal surfaces.

Can I repair microwave sparking myself?

Basic fixes like replacing the waveguide, turntable, or cleaning debris can be DIY. However, repairs to components like diodes and magnetrons require professional service to avoid high voltage dangers.

How can I prevent microwave sparking?

Keep the unit clean, never put metal in the microwave, and replace worn parts promptly. Use microwave-safe containers only. Follow manufacturer instructions carefully.

When should I replace vs repair my sparking microwave?

For newer microwaves under 5 years old, replacement parts can fix most sparking issues. With older microwaves over 10 years old, replacement is likely the safer and more cost-effective option when sparks appear.


While startling, most microwave sparking issues can be resolved with simple repairs and care. Common culprits include:

  • Damaged waveguide cover
  • Worn turntable rings
  • Metal objects like foil inside
  • Faulty diode
  • Failing magnetron

Thorough microwave cleaning, inspection of parts, and replacement of worn items can eliminate sparks in many cases.

However, sparking in an older microwave may indicate it’s time for retirement and replacement with a new model for ensured safety. With some diligence, you can determine the cause of microwave sparking and take appropriate action.

By Rosie Elliott

I’m Rosie. I’m a professional chef with experience in Western, Mediterranean, and Italian cuisine. I’ve been cooking for over 15 years, and I have two daughters that keep me busy!

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