A microwave that stops working usually shows one of a few symptoms: it’s completely dead, it runs but doesn’t heat, it sparks, or the keypad stops responding. Some causes you can check in a minute. Others sit behind the cover, where a microwave stores a dangerous high-voltage charge even when it’s unplugged. This guide tells you which is which.
Safety first: never remove the outer cabinet of a microwave. The high-voltage capacitor inside can hold a lethal charge after the unit is unplugged. The checks below are all from the outside.
Microwave Completely Dead: No Light, No Display
- Check the outlet and the breaker. Plug a lamp into the same outlet. Kitchen outlets are often on a GFCI that trips and shuts off the whole circuit, so press the reset button.
- Over-the-range microwaves are plugged in inside the cabinet above. Check that the plug hasn’t come loose.
- Unplug it for a minute, then plug it back in. A power surge can lock up the control.
If the outlet works and the microwave is still dead, the usual causes are a blown internal fuse, a thermal fuse or a failed door switch. A fuse often blows because a door switch has failed, so simply replacing the fuse doesn’t fix the problem. These are technician repairs.
Microwave Runs but Doesn’t Heat
The light is on, the plate turns, the fan runs, but the food stays cold. This is the most common microwave fault. Try this first:
- Heat one cup of water for one minute on full power. If it barely warms, the heating circuit has a problem.
- Make sure the microwave isn’t set to a low power level, a defrost mode or a demo mode. Demo mode is described in your manual.
The causes are inside the high-voltage circuit: the magnetron, the high-voltage diode, the capacitor or a door switch. A technician has to test them. On a basic countertop microwave, replacing it is often cheaper than this repair. On an over-the-range or built-in microwave, the repair is usually worth doing.
Sparking or Arcing Inside
- Metal in the cavity: foil, a twist tie, a mug with metallic trim or a metal rack that doesn’t belong to the oven.
- A dirty or burnt waveguide cover. This is the small panel on the inside wall, usually mica. Food splatter on it can burn and spark. Clean it gently. If it has a burnt spot, it has to be replaced.
- Chipped paint inside the cavity. Bare metal can arc.
Stop using the microwave while it’s sparking. Arcing that keeps going can damage the magnetron.
Buttons Don’t Respond
- Check for child lock (often activated by holding Cancel or Stop for a few seconds; see your manual).
- Steam and grease can get behind the touchpad. Unplug the unit, wait and try again.
- If only some buttons work, the touchpad or control board is failing.
Turntable Doesn’t Turn
Make sure the glass tray sits correctly on the roller ring and that nothing is under it. If it’s seated properly and still doesn’t turn, the turntable motor or its coupler is worn. That’s a fairly simple repair.
Loud Humming, Grinding or Buzzing
A soft hum is normal. A new loud buzz, a grinding sound or a burning smell while heating can mean a failing magnetron, diode or fan motor. Stop using it and have it checked. Learn more about using and maintaining a microwave so the problem doesn’t come back.
Door Problems
A microwave won’t start if a door switch thinks the door is open. A worn latch, a broken hook or a door that doesn’t close flush is a common cause of a microwave that won’t start. Don’t use a microwave with a damaged or warped door.
Repair or Replace?
- Over-the-range and built-in microwaves are worth repairing in most cases. Replacing them also means mounting and venting work.
- Countertop microwaves: a door switch, turntable motor or fuse can be worth fixing. A failed magnetron in an inexpensive model usually isn’t.
Frequently Asked Questions
Why did my microwave stop working suddenly?
The most common reasons are a tripped GFCI outlet or breaker, a blown fuse caused by a failed door switch, or an overheated thermal fuse. Check the outlet first.
Why is my microwave running but not heating?
Usually a failed magnetron, high-voltage diode or capacitor, or a door switch. These parts are in the high-voltage circuit and have to be tested by a technician.
Can I fix a microwave myself?
You can check the outlet, the settings, the turntable and the waveguide cover. Anything that requires opening the cabinet should be left to a trained technician because of the stored high voltage.
Is it safe to keep using a microwave that sparks?
No. Stop using it, remove any metal, and clean the inside. If it still sparks, have it inspected.
Need Your Microwave Repaired?
We repair countertop, over-the-range and built-in microwaves for brands including GE, Whirlpool, Samsung, LG, KitchenAid, Frigidaire, Bosch, Wolf and Thermador, in Sacramento, West Sacramento, Davis, Woodland, Dixon, Vacaville, Elk Grove and Rancho Cordova. See all our appliance repair services, call (510) 677-7166 or book online. The service call is $80, and same-day service is available.
