Your Microwave Comes On When the Door Is Opened—Here’s Why

You go to heat up your leftovers in the microwave, but when you open the door, you notice the familiar hum of a running microwave. You haven’t pressed any buttons, but the fan is going, and now, you’re concerned about the microwaves coming out of the appliance. Here are some common reasons why a microwave comes on when the door is opened, plus what you can do to solve the problem.

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1. The Door Switch Is Jammed

Microwaves have a door switch as an added safety feature. This switch triggers when the door opens and keeps the microwave from running. So, if the microwave comes on when the door is opened, the most likely problem is a faulty door switch. The switch could be jammed by food or other debris. 

Shut the door and unplug the microwave. Then, check around the microwave door to see if there is any buildup or other debris. Clean out any debris; however, if something is lodged into the switch, you may need to hire an appliance repair pro to come inspect and clean out the switch.

2. A Faulty Switch Is Shorting the Magnetron

The magnetron is responsible for creating the microwaves that heat your food. But if the door switch is faulty, it can cause the power to the magnetron to short. If that happens, you may notice that the microwave fan comes on when the door is opened. A failing magnetron could also cause loud buzzing.

If the microwave is running when the door is open, you may need to unplug it and turn it off at the circuit breaker until an appliance repair pro can come inspect the microwave and replace the door switch and/or the magnetron.

Don’t attempt to change microwave parts on your own. Because microwaves contain a high-voltage capacitor, which retains voltage even when you unplug the appliance, they pose a shock or electrocution risk. Leave all microwave repairs to the pros.

3. The Light Is On for Convenience

If the microwave light comes on when you open the door, that’s a good sign that your microwave is working as intended. The light is handy, making it easier to see the inside as you grab your hot food. If only the light is coming on and not the fan when you open the door, your microwave is functioning properly.

4. The Fan May Be Broken

Microwave fans don’t typically run when the door is open, so if you notice that the microwave fan comes on when the door is opened, it may be an issue with the fan. To test if it’s just the fan, you can place a microwave-safe container of water inside the microwave, and keep the door open just a crack. Stand away from the microwave during this test. After about one minute, check to see if the water is warmer. 

If the water is warmer, it means the microwave is emitting microwaves while the door is open, and the problem is not just the fan. However, if the water doesn’t get warmer, you may have a faulty fan that needs to be replaced by a pro.

5. The Control Board May Be Faulty

If the microwave continues running after you open the door, there could be an issue with the microwave control board. Another sign of a faulty control board or wiring is when the microwave keeps tripping the breaker.

Because this is an electrical issue, it’s best to hire someone who repairs microwaves, such as an electrician, to inspect the appliance. It also may be worth it to replace the microwave altogether if a major part fails rather than pay for a new part.

What to Do If Your Microwave Runs With the Door Open

From the microwaves emitted by the magnetron to the high voltage in the capacitor, microwaves can pose multiple health and safety risks, so this isn’t a problem to ignore or try to work around. 

If your microwave comes on when the door is opened, hire a microwave pro near you to inspect the appliance and determine whether it’s best to repair or replace the microwave. If your microwave is around 5 years or older, it’s time to budget around $100 to $200 for the cost to install a new microwave.