Microwave Won’t Turn Off? Here’s Why

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Microwaves are now in nearly every home. They are a must-have appliance that many people use to help them cook. When they stop working as they are supposed to, it can be annoying and costly if you have to repair or replace them.

One way microwaves can stop working correctly is when they won’t turn off when they are supposed to. It doesn’t happen that often, but it can happen. The good news is this problem is only caused by a couple of possible faulty components, so it’s quite straightforward to find the cause of the problem and fix it.

If your microwave won’t turn off, the cause may depend on whether the microwave door is open or if the door is closed.

  • The microwave won’t turn off when the door is open. If your microwave still operates even when the door is open, this is a good sign that the door interlock switch is faulty. The switch is meant to send a signal to the control board to turn the microwave off when the door opens, so when it becomes faulty, it won’t be able to do this. This is very dangerous, and you should cease using your microwave at all until it is fixed.
  • The microwave won’t turn off when the door is closed. If the microwave keeps running only when the door is closed and after you’ve pressed the stop button, this most likely means that it’s a control board problem. If the microwave immediately stops when the microwave door is opened, then this indicates a problem with the switch in the door and the control board not receiving the correct signals. Either way, the control board will need to be replaced.

So, if your microwave won’t turn off, there are two parts that you have to test and repair: the door interlock switch and the control board. All you have to do is follow our step-by-step guide below to diagnose and fix each component.

Microwaves are extremely dangerous to work on due to the risk of electrical shock. We highly recommend only people with the proper training undertake the tests we have outlined below. If in doubt, you should contact a qualified technician to help you with this repair.

Test the Door Interlock Switch

The door interlock switch is responsible for supplying power to other components in your microwave, and when the door opens, it shuts off power to these components, effectively shutting the microwave off. The switch is activated by a hook or latch that is on the door. When the switch fails, your microwave will keep working even when you open the microwave door.

Here’s how to test the door interlock switch:

  1. Start by making sure that the power is disconnected to your microwave. As mentioned above, working with microwaves is extremely dangerous, and you should only attempt this test if you are qualified to do so.
  2. Next, locate the door interlock switch and remove it from the microwave (you will probably have to remove the microwave’s cabinet to get access to it).
  3. Once removed, use a multimeter to test the switch for continuity. The multimeter should be set to Rx1. Place the probes on the terminals, and first test the switch without the button pushed in. This test should indicate the switch has continuity. You can then test it again with the button not pushed in, which should show the switch doesn’t have continuity.
  4. If either of those two tests fail, you should replace the door interlock switch.
  5. Once replaced, plug the microwave back in and check if the problem has been solved. If your microwave still won’t turn off, you should consider purchasing a new one.

Test the Control Board

The control board controls your microwave by sending power to the relays. When your microwave keeps working even after you press the “stop” button, this is a good sign the control board is faulty. It is possible to keep using a microwave even when this occurs, but it’s not ideal – you should replace the control board.

Here’s how to test the control board:

  1. Make sure that the microwave is turned off from its power source. Again, only attempt this repair if you are qualified to do so.
  2. Locate the control board. You will have to remove the microwave cabinet to get access to it. The control board is usually located right behind the keypad.
  3. Inspect the control board for any signs of burning or damage. If you find obvious damage, you should replace the control board.
  4. If there is no obvious damage, you need to test the board with a multimeter. Set your multimeter to Rx1 and then place the probes on the output terminals of the relay and test it for continuity.
  5. If the test shows no continuity, you will need to replace the control board.
  6. Once replaced, check to see if the problem has been fixed. If your microwave still won’t turn off, you should purchase a new one.
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