Microwave Sparking? Causes, Quick Fixes and Safety Rules

Microwave sparking is caused by metal or something conductive in the cavity, or by damage to the interior. Stop the microwave at once, open the door, and remove the cause: foil, a metal-trimmed plate, a fork, a twist tie, or burnt food. If it sparks with only a cup of water inside, the microwave is damaged. Do not keep using it.

Microwave sparking: first steps

1. Stop the microwave by opening the door or pressing stop. Unplug it if sparks continue.
2. Remove the food and container, and check for any metal.
3. Let it cool, then look inside with a flashlight.
4. Do not run it empty. Running an empty microwave can damage the magnetron.

Quick facts: microwave sparking
First action	Stop, then remove anything metal
Common causes	Metal, burnt food, damaged waveguide cover, scorched interior
Safe test	Heat a cup of water for 30 seconds and watch
Never	Open the casing; the capacitor can hold a lethal charge

What causes the sparks

Cause	Why it sparks
Foil, twist ties, metal-trimmed plates	Metal reflects microwaves and arcs
Forks, spoons, travel mugs	Same, especially pointed edges
Food splatter and grease	Carbon deposits conduct and arc
Damaged waveguide cover	The cover protects the opening; burnt food can scorch it
Scratched or chipped interior	Exposed metal arcs
Some foods	Grapes cut nearly in half, and some vegetables high in minerals, can arc

Fixes you can do safely

1. Remove metal and any container with metallic paint or trim.
2. Clean the cavity. Wipe away food, grease and carbon marks. A bowl of water with lemon heated for a few minutes loosens grime.
3. Check the waveguide cover, the small, usually mica or plastic panel on the side wall or ceiling. If it is burnt, cracked or dirty, replace it. They are cheap and fit with a screw or clip.
4. Look at the interior paint. Chipped or bubbled paint on the walls can expose bare metal. Small chips can sometimes be touched up with microwave-safe paint, but heavy damage means replacement.
5. Test with a cup of water. Heat it 30 seconds. If it sparks again with nothing else inside, stop using the microwave.

What not to do

• Do not use a microwave that sparks with only water in it.
• Do not open the housing or attempt electrical repairs; the capacitor retains a high-voltage charge even when unplugged.
• Do not tape over damage or use foil to cover problems.
• Do not run it empty to see whether the sparking has stopped.

When a microwave sparking problem means replace it

A scorched waveguide cover is an easy repair. But if the cavity walls are burnt through, the paint is peeling, there is a burning smell, or it sparks with water only, the microwave is not safe. Most countertop models are cheaper to replace than to repair, and a built-in unit should be assessed by a technician.

Foods and containers that spark

Never use foil, metal-rimmed plates, takeaway containers with metal handles, or travel mugs. Avoid grapes sliced almost in half, and cover foods to stop splatter. Use only containers marked microwave-safe.

What the waveguide cover looks like

The waveguide cover is a thin rectangular or round panel inside the cavity, often on the right wall or the ceiling, held by a small screw or clip. When it is burnt it looks brown or black, or has pits and holes. Replace it with the exact part for your model; they are inexpensive. Do not substitute cardboard or plastic, since the cover must be made of a material that microwaves pass through.

Prevention

Wipe the cavity weekly, cover food, and replace the waveguide cover if it darkens. Keeping the microwave clean reduces carbon build-up that can cause microwave sparking.

Microwave sparking: stop the cycle first

If a microwave sparking inside the cavity, stop it at once and unplug it. Sparks usually come from metal, such as foil, a fork or a gold-rimmed plate, or from a damaged waveguide cover. Remove the object and check the cavity walls for burn marks. A microwave sparking near the top of the cavity often points to a chipped waveguide cover, which is a small part but should be replaced. Do not operate the microwave with a damaged cover, and do not open the outer cabinet, which contains high-voltage parts.

Related reading

• Microwave Not Heating? Safe Checks and When to Replace It
• Oven Not Heating? Bake Element, Sensor and Fuse Checks
• Refrigerator Making Loud Noise? Normal Sounds vs Real Faults
• Electric Stove Burner Not Working? Coil, Socket and Switch Tests

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