Microwaves are so routine that it's easy to forget there's a high-voltage power supply and a magnetron inside the cabinet. They're built with multiple safety features, and when those are in good shape, using one is very safe. The checks below help you notice when something has stopped working the way it should, and the list at the end covers what not to put inside.
The door
The door is the most important safety part of a microwave. Federal rules require microwaves to have at least two operating safety interlocks that shut off microwave energy when the door opens.
- Open the door mid-cycle. The microwave should stop immediately.
- Check that the door closes firmly and latches without force.
- Look at the door seal and the surface it presses against. Keep them clean; food residue can stop the door closing fully.
- Look for dents, cracks or warping. The EPA advises against using a microwave if the door appears dented or broken, or if the hinges or latches are damaged.
If the microwave runs with the door open, or the door is damaged, stop using it.
Sparking and arcing
Sparks inside a microwave usually come from one of a few causes:
- Metal inside. Foil, twist ties, metal-trimmed dishes and some take-out containers can arc.
- A damaged waveguide cover. This is the small panel, often mica, on an inside wall. If it's burned, greasy or broken, food splatter behind it can arc.
- Chipped interior paint. Exposed metal in the cavity can spark.
- A damaged rack. Some microwaves come with a metal rack designed for them; if the coating is chipped, it can arc.
If you see sparks, stop the microwave. Clean the interior, including the waveguide cover. If arcing continues with nothing inside but a cup of water, have it inspected.
Never heat these
- Metal of any kind, unless the manual specifically allows it.
- Sealed containers or jars, which can burst.
- Eggs in the shell.
- Plastic not labeled microwave-safe.
- Paper bags, newspaper or recycled paper products.
- Nothing at all. Running a microwave empty can damage it.
Superheated water
Water heated in a smooth container can go past boiling without bubbling, then erupt when moved. Don't overheat water, let it sit briefly before removing it, and use a container with a slightly rough interior or add a microwave-safe stir stick.
Cleaning without damage
- Heat a bowl of water with a splash of vinegar or lemon for a few minutes, then wipe the softened splatter off the walls and ceiling.
- Pay attention to the ceiling and the waveguide cover; splatter there is what usually causes arcing later.
- Use a soft cloth, not steel wool or an abrasive pad, which can scratch the interior coating.
- Don't spray cleaner into vents or around the control panel.
- Wash the turntable and its roller ring and check that the ring isn't cracked.
Placement and power
Countertop microwaves need clearance at the vents, usually on the sides, top or back, so check the manual before tucking one into a cabinet nook. Plug it directly into a wall outlet rather than a power strip, and if it shares a circuit with a toaster oven or kettle, expect a tripped breaker sooner or later.
Over-the-range microwaves
An over-the-range microwave doubles as a range hood, so it has a fan, lights and a grease filter in addition to everything else.
- Clean or replace the grease filters underneath regularly.
- Replace the charcoal filter if it recirculates air instead of venting outside.
- Check that it's securely mounted. It shouldn't move when you open the door.
- Don't store things on top of it, and don't leave a pot boiling hard under it for long periods without the fan on.
Fire inside the microwave
Keep the door closed, turn it off and unplug it if you can safely. The fire should go out without oxygen. If it doesn't, or spreads, get out and call 911. Our guide to handling kitchen fires covers this and other kitchen emergencies.
Repairs: leave the cabinet closed
Microwaves contain a high-voltage capacitor that can hold a dangerous charge even after unplugging. Don't open the cabinet yourself. If your microwave doesn't heat, the turntable won't spin, the door won't latch, it trips a breaker, or it sparks, book a microwave repair visit. Over-the-range and built-in units are usually worth repairing; countertop units often aren't, and we'll tell you if that's the case. Search your model on the CPSC site too, as our recall lookup steps explain.
The quick test, monthly: open the door mid-cycle and confirm it stops. That one check covers the most important safety feature.