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Why does my microwave run but not heat?
A microwave that runs but won't heat usually has a failed magnetron, high-voltage diode, high-voltage capacitor, or door switch. These parts make or control the energy that heats food. The light and turntable run on a separate circuit, so they can work even when heating has stopped.
It helps to know how a microwave works. A high-voltage circuit powers the magnetron, which makes the microwaves that heat your food. If any part of that circuit fails, the oven seems to run normally but nothing gets hot.
Is it safe to repair a microwave yourself?
No, not inside the cabinet. The high-voltage capacitor can store a dangerous electrical charge even after the microwave is unplugged. Opening the cover without training and the right tools can cause a serious shock.
The FDA's microwave oven safety page also warns not to use a microwave if the door does not close firmly or is bent, warped, or damaged, and to stop using it if it keeps running with the door open.
Microwave not heating or sparking? Stop using it and call us. A technician can safely test the high-voltage parts.
What can you safely check?
- Test with a cup of water. Heat one cup for one minute on high. If it is barely warm, the oven is not heating properly.
- Check the power setting. Make sure it was not left on a low power level or a demo mode.
- Close the door firmly. A worn latch or door switch can stop heating while the light still works.
- Check the outlet. Microwaves need a dedicated, properly working circuit. Try resetting the breaker.
- Look for a recall. Search your model on the CPSC recall list.
What are the most common failed parts?
Magnetron
The magnetron makes the microwaves. When it fails, the oven runs but does not heat, sometimes with a loud hum or buzz.
High-voltage diode and capacitor
These parts boost the voltage that powers the magnetron. A failed diode is one of the most common reasons a microwave stops heating.
Door switches
Microwaves have several door switches for safety. If one fails, the oven may not heat, may blow a fuse, or may not start at all.
Main control board
A failed control board can stop the heating circuit even when the display and buttons seem to work.
What should you do with food in the meantime?
If your microwave is heating unevenly or weakly, food may not reach a safe temperature. Use your stove or oven instead until it is fixed, and check reheated food with a thermometer.
The USDA's guide to cooking safely with microwave ovens explains why cold spots matter and how to heat food evenly.
Repair or replace your microwave?
Over-the-range and built-in microwaves are usually worth repairing, because replacing them also means removing and installing a heavy unit. Countertop models under a few years old may be worth fixing too, but low-cost ones are often cheaper to replace. Our repair or replace guide walks through the decision.
Our microwave repair service covers over-the-range and built-in models from Sharp, Panasonic, GE, Whirlpool, Samsung, LG, Wolf, and Thermador. See typical prices in our repair cost table.
Frequently asked questions
Why does my microwave run but not heat?
The most common causes are a failed magnetron, high-voltage diode, high-voltage capacitor, or a door switch. A blown internal fuse can also stop heating on some models.
Can I fix a microwave myself?
Only the simple checks. A microwave's high-voltage capacitor can hold a dangerous charge even when it is unplugged, so internal repairs should be done by a trained technician.
Is it worth repairing a microwave?
Built-in and over-the-range microwaves are often worth repairing because they cost more to replace and install. A low-cost countertop microwave is usually cheaper to replace.
