Microwave won't turn off

When a microwave won't turn off, the most likely cause is a failed microwave door switch, especially if the fan keeps running after you open the door. Most models use three or four switches, including the primary door switch, secondary door switch, and monitor switch, which must actuate in sequence when the door closes. Test each switch for continuity, and replace any switch that fails. Next, the user control and display board may have a cancel or off button that is no longer registering. If all control panel buttons are unresponsive, replace the user control and display board. If only some buttons fail, the touchpad and control panel or the separate membrane touchpad is more likely defective. Less commonly, a stuck relay or triac on the main control board can keep the microwave fan or other components running. Enter your model number to find the exact replacement part for your microwave. Any repair that requires opening the outer cabinet carries a serious shock risk because the high-voltage capacitor can store lethal charge even after the microwave is unplugged. It must be properly discharged before interior work, so use a qualified technician if you are not familiar with capacitor discharge procedures.

01 - Microwave Door Switch

Most microwaves have three or four door switches. When the microwave door closes, the door switches actuate in sequence to ensure that the door is closed properly. If any of the door switches fail, the microwave will not start or heat. In some rare cases a door switch may short out and allow the fan to run even when the door is opened. To determine if any of the door switches are defective, use a multimeter to test each of the switches for continuity. If any of the door switches lack continuity, replace the switch. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even ...after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace a door switch.)

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02 - Microwave User Control and Display Board

The cancel or off button on the user control and display board may not be activating. To determine if the control and display board is defective, try pressing each of the buttons on the control panel. If none of the buttons are responding correctly, replace the user control and display board.

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Highly Likely

03 - Microwave Touchpad and Control Panel

The cancel or off button on the control panel may not be activating when it's pressed. To determine if the touchpad and control panel are defective, try pressing each of the buttons on the control panel. If some of the buttons respond correctly while others don’t, replace the touchpad and control panel.

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Common

04 - Microwave Touchpad

The cancel or off button on the touchpad may not be activating. To determine if the touchpad is defective, try pressing each of the buttons on the control panel. If some of the buttons respond correctly while others don’t, replace the touchpad.

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Common

05 - Microwave Main Control Board

The main control board has relays that send power to several components to make the microwave work. If one or more of the relays or triacs short out, some of the components can keep running when the controls are turned off. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the main control board.)

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Common

06 - Microwave Control Board

The control board has relays that send power to several components to make the microwave work. If one or more of the relays or triacs short out, some of the components can keep running when the controls are turned off. While you can often replace just the control board, some microwave models sell control panels as an assembly with both the touchpad and control board included.

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Uncommon But Possible