Microwave Sparking Inside? Causes and What to Do

A microwave sparks when microwave energy concentrates on metal or a damaged spot. Stop it, unplug it and let it cool. Then remove any foil, gold-trimmed dishes, twist ties or metal utensils, and clean food residue from the walls. Check the small waveguide cover and the paint. If sparks continue with an empty, clean oven, call a technician.

Arcing looks alarming, and it can damage the oven. Most of the time the cause is something simple you can fix in a few minutes.

Why is my microwave sparking?

• Metal in the oven. Foil, forks, twist ties, takeout containers with metal handles and plates with gold or silver trim are the usual causes.
• A burnt or greasy waveguide cover. This is the small panel, often on the side wall, that protects the opening where the microwaves enter. Grease or burn marks on it can arc.
• Chipped paint or exposed metal. Paint on the cavity wall can wear away. Food splatter on bare metal then arcs.
• A worn turntable support or stirrer. If a plastic part has worn through, the metal underneath is exposed.
• Food that arcs by itself. Small watery pieces, such as grapes close together, can spark.
• A failing internal part. A weak magnetron or a bad high-voltage diode can cause sparks, and they need a technician.

What the pattern tells you

How to fix it

1. Stop the microwave and unplug it. Leave the door shut if there is any smoke. Let it cool for several minutes.
2. Take out everything inside. Look for foil, a twist tie, a fork or a plate with a metal rim.
3. Clean the walls and ceiling. Wipe with a damp cloth and a little dish soap. Grease and burnt food are a main trigger.
4. Check the waveguide cover. Look at the small panel on the inside wall. If it is warped, burnt or has a hole, replace it. It is a cheap part, and models vary, so look up yours by model number.
5. Look at the paint. Small chips can be touched up with a microwave-safe appliance paint. Large patches of bare metal mean the oven is wearing out.
6. Inspect the turntable and its support. Replace a cracked or worn one.
7. Run it with a cup of water. Put a microwave-safe cup of water inside and run it for 30 seconds. If there are no sparks, the cause was metal or residue.

Should I keep using it?

If the sparks stopped after you removed metal and cleaned the cavity, yes. If you see damaged paint, a burnt waveguide cover or arcing that returns, stop until it is fixed. Continued arcing can burn a hole in the cover or damage the magnetron, which turns a cheap repair into an expensive one.

Is it worth repairing?

A waveguide cover or a turntable part costs little and is worth replacing. A magnetron or diode costs more, and a countertop microwave is inexpensive to replace. Get a quote, then compare it with a new unit, especially if yours is more than 8 to 10 years old. For a built-in or over-the-range model, repair is more often worth it because of the installation work.

When to call a professional

Call a technician if:

• It sparks with nothing inside and a clean cavity.
• You see burn marks, melted plastic or smell burning.
• It makes a loud buzz or hum while it sparks.
• The microwave trips the breaker, or has stopped heating, as in a microwave that is not heating.
• The door does not close properly, as covered in a microwave that keeps running with the door open.

What not to do

• Do not run the microwave empty.
• Do not use foil or metal-trimmed dishes.
• Do not use a microwave with a hole in the waveguide cover.
• Do not open the back panel.

Bottom line

Remove metal, clean the oven and check the waveguide cover. Those three steps solve most sparking. If it sparks when it is empty and clean, retire it or call a technician. If your microwave also shuts itself off, read why a microwave keeps shutting off. For smoke from the other kitchen appliance, see smoke from an oven.