Microwave sparking or arcing inside
Sparks inside a microwave, also called arcing, happen when microwave energy finds metal or a burned spot to jump across.
Urgent Sparking can scorch the cavity, damage the microwave and start a fire, so stop the cycle at once and do not use the microwave again until the cause is found.
What this symptom usually means
Sparks inside a microwave, also called arcing, happen when microwave energy finds metal or a burned spot to jump across. The causes manufacturers list first are things you can see. LG, Samsung and Whirlpool all list metal first: foil, twist ties, staples, metal utensils, and dishes with gold or silver trim. A metal rack that touches the cavity wall will spark; LG says the rack must sit on all four of its plastic supports, and Whirlpool says a convection rack or crisper pan must not touch the walls, ceiling or floor. Food splatter that has baked onto the walls or the cover can carbonise and spark. LG adds that running the microwave empty can cause sparking, and Whirlpool notes some vegetables with a high mineral content can arc on their own.
If none of those apply, the microwave itself may be damaged. The small panel on the cavity wall covers the opening where the microwaves enter; Samsung Canada calls it the magnetron cover (it is also called the waveguide cover) and says removing or damaging it can cause sparking. LG says damage to the interior of the cavity can cause arcing and that the microwave should then not be used until it is serviced. Beyond that, the cause is inside the cabinet, and that is off-limits: GE warns that a microwave's high-voltage capacitor can hold a dangerous charge even after it is unplugged.
Checks you can do yourself
- Stop it nowPress Stop or Cancel as soon as you see sparks, and unplug the microwave if you can reach the plug safely, or switch off its breaker. Let it cool before looking inside.
- Look for metalRemove foil, twist ties, staples, metal utensils and any dish with gold, silver or metallic trim or glaze. Whirlpool also lists pewter and meat thermometers that are not approved for microwave use.
- Racks and pansIf your microwave has a metal rack, make sure it sits on all four plastic supports and does not touch the walls (LG). On convection or combination models, Whirlpool says metal bakeware is for the oven functions only, and racks and crisper pans must not touch the cavity walls, ceiling or floor.
- Turntable in placeCheck the glass turntable is seated on its coupler. Samsung lists running without the turntable in place as a cause of sparking.
- Clean the cavityWith the microwave unplugged and cool, clean food splatter from the walls, ceiling and rack supports (Whirlpool, LG). Clean the cover panel gently with a soft cloth and mild detergent; Samsung Canada says not to scrub it hard and not to remove it.
- Look for damageWith a light, look at the cover panel and the cavity walls for burn marks, holes, chipped coating or rust. If you see any, stop: LG and Samsung both say damage inside means service, not more use.
- Never run it emptyWhen you next test it, put a cup of water inside (LG suggests about 250 mL, or 8 oz). Only test once metal, soil and racks have been dealt with, and stop again at the first spark.
Nothing above involves gas, wiring, refrigerant or removing panels.
What you notice, and what it can point to
Listed in no particular order. They help you describe the problem; only an inspection confirms the fault.
Sparks at the rim of a plate or bowl
Could point to: Metallic trim or glaze on the dish (LG, Samsung)
Next step: Stop, and use plain microwave-safe cookware
Sparks where a metal rack meets the wall
Could point to: Rack not seated on its supports, or a support is broken (LG)
Next step: Reseat the rack; book if a support is damaged
Sparks from one spot on the wall or the cover panel
Could point to: Baked-on food on the wall or cover, or a damaged cover (Whirlpool, Samsung)
Next step: Unplug, let it cool, clean gently; book if the cover is burned or holed
Sparks with nothing metal inside, near a chipped or rusty spot
Could point to: Damage inside the cavity (LG)
Next step: Stop using it and book
Sparks during a convection or air-fry program
Could point to: Metal accessory used in microwave mode or touching the cavity (Whirlpool)
Next step: Check the manual for which accessories go with which mode
Sparks when heating certain vegetables
Could point to: High mineral content in the food (Whirlpool)
Next step: Stop the cycle; book if it happens with other foods
How it differs by design
Countertop. Sparking causes are the same, but the repair decision is different. A basic countertop unit may not justify a visit once the cavity or magnetron is damaged; we say so before you book if you send the model number.
Over-the-range and built-in. These are installed into cabinetry and some come with metal racks. Over-the-range units also act as the range hood, so a damaged unit leaves the cooktop without ventilation as well.
Convection and combination models. Whirlpool says metal bakeware and racks are for the oven functions (bake, air fry, toast), not microwave mode, and must not touch the cavity.
Covers vary by model. Where the panel over the microwave inlet sits varies by model. Samsung Canada calls it the magnetron cover; it is also called the waveguide cover. On all of them it stays in place.
What our technician checks
These need panels off, live electrical tests or a licensed trade, so they are left to the technician:
- Removing the outer cabinet or any panel other than the ones the manual tells you to clean
- Anything to do with the high-voltage capacitor, transformer, diode or magnetron; GE warns the capacitor can hold a dangerous charge after unplugging
- Removing, replacing or trimming the waveguide cover
- Door, hinge, seal or interlock work of any kind (Health Canada: do not tamper with the safety interlocks)
- Disconnecting a hard-wired built-in unit
Waived when you go ahead with the repair. You get the cause, the price and our repair-or-replace verdict in writing before any work.
Repairs a technician may recommend
After inspection, not from the symptom alone.
Waveguide (magnetron) cover replacement
When the cover is burned, holed or saturated with grease. The technician checks the area behind it for damage at the same time.
Cavity repair or coating touch-up
When chipped coating or rust in the cavity is arcing. Whether it can be repaired depends on the extent and on what the maker supplies.
Rack support replacement
When the plastic supports that keep a metal rack off the walls are broken (LG).
Magnetron or high-voltage component replacement
When prolonged arcing has damaged the magnetron or the high-voltage circuit. The technician discharges the capacitor before any test.
Stirrer or turntable drive repair
When a stirrer cover or turntable coupler is damaged and no longer distributes energy as designed.
Replacement recommendation
When the cavity is badly damaged or the unit is a lower-value countertop model. The finding says so before any work.
Brands we see with this problem
Codes, parts and access differ by brand; the brand pages cover where the model label is and what to expect.
Cost, and whether to fix it
What the repair costs depends on the part, the labour and whether a second visit is needed for an ordered part; the written finding gives the total before any work. Our guides on what drives repair costs and repair versus replacement explain how to weigh it.
When to book
Book when sparks continue with no metal inside, the racks seated and the cavity clean, or straight away if you see burn marks, a damaged cover panel, chipped coating or rust. Tell us the type (countertop, over-the-range, built-in or drawer), the brand and model, where in the cavity the sparks appear, and what was inside at the time. For a built-in or over-the-range unit the written finding compares repair with replacement; for a countertop model we will say from the model number whether a visit makes sense before you book. The diagnostic is $89 (+tax), waived if you go ahead, with a written finding and quote before any work. See microwave repair.
We handle this across Ottawa and Gatineau
Related problems
Microwave sparking or arcing inside: questions
Is a spark in the microwave dangerous?
It can be. Sparking can scorch the cavity, damage the microwave and ignite food or packaging. Stop the cycle at once. Whirlpool warns that prolonged arcing can damage the oven.
There was no metal inside. Why did it spark?
Other causes manufacturers list are baked-on food on the walls or cover, a rack touching the wall, running it empty, or damage inside the cavity. LG and Samsung both say that if sparking continues after those are ruled out, the microwave needs service.
Can I replace the waveguide cover myself?
We do not give instructions for it. Samsung Canada says the cover is a permanent part and that removing or damaging it can cause sparking. A burned cover can also mean damage behind it, which a technician should see.
Why is it unsafe to open a microwave?
GE says it gives no do-it-yourself repair advice on microwaves because the internal high-voltage capacitor can hold a charge after unplugging. Health Canada advises using qualified service technicians for all adjustments and repairs.
Is it safe to use metal racks in my microwave?
Only the rack that came with it, placed as the manual says. LG requires the rack to sit on all four plastic supports. Whirlpool says metal bakeware belongs in the oven modes of combination models, not in microwave mode.
Some vegetables spark when I heat them. Is that a fault?
Whirlpool says some vegetables with a high mineral content can arc on their own. Stop the cycle and do not let it continue. If sparking happens with other foods too, book.
Sources
- LG USA: Why is my microwave arcing or sparking?
- LG USA: LG microwaves, how to prevent sparking
- Whirlpool Product Help: General arcing and sparking, over-the-range microwave
- Samsung Canada: Why is there plastic film or a cardboard-like cover inside your Samsung microwave?
- Samsung Canada: Samsung microwave FAQs
- Samsung Gulf: What to do if my Samsung microwave is sparking during operation
- GE Appliances: Microwave runs but does not heat (high-voltage capacitor note)
- Health Canada: Microwave ovens
Sources checked 2026-09-24.
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- $89 diagnosticWaived when you go ahead with the repair
- Written finding on every visitCause, price and our repair-or-replace verdict
- 90-day warrantyOn labour and the parts we install