Microwave Not Heating? Here’s What to Do

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Is your microwave not heating? In this article, we will discuss the most common causes of the problem and how you can solve each one.

Before you get started, it’s important to note that working with microwaves is extremely dangerous if you are not trained or experienced in doing so. Make sure that the power is switched off and that you discharge the high voltage capacitor before you start checking the components in the microwave for faults.

Door Switch

The first component to check is the door switch. The door switch ensures that the microwave can’t operate when the door is not closed properly. Over time the door switch can wear out, and this will stop your microwave from operating correctly.

To check if the switch needs to be replaced:

  1. Turn the power on.
  2. Open the door and see if the light comes on in the microwave.
  3. Close the door and see if the light turns off or not. If the light stays on, then the door switch is likely defective and needs to be replaced.
  4. You can also check the switch with a multimeter to double-check if it needs to be replaced.
  5. To check the switch with a multimeter, first turn the power back off, and then take the microwave case off by unthreading the screws that hold it in place.
  6. Locate the door switch and use a multimeter to check the switch for continuity.
  7. If the switch has continuity, then it is working correctly, and if not, it is faulty and needs to be replaced.
  8. If you replace the door switch, you should then put the microwave back together, plug it in, and check if the problem has been solved.

High Voltage Diode

The next component to check is the high voltage diode. The role of the high voltage diode is to convert your A/C power supply into D/C power so that the magnetron can operate. The most obvious sign it is defective is if you can hear a buzzing sound or humming sound coming from the microwave when it’s turned on.

To check if it needs to be replaced:

  1. Make sure the power is switched off.
  2. Remove the case off the microwave if you haven’t already.
  3. Locate the diode and check for any visible signs that it is burnt out, and if it is, you will need to replace it.
  4. If it doesn’t look burnt out, then use a multimeter to check it for continuity.
  5. The diode should have a higher resistance on one end and a lower level of resistance on the other end. If the test shows this to not be the case, then it will need to be replaced.
  6. Once you replace the diode, you can put the microwave back together and then test if the problem has been solved.

Magnetron

The magnetron is the main component in your microwave that produces the radiation required to make it function. Sometimes the magnetron can become defective, or the fuse blows and needs to be replaced.

To check the magnetron:

  1. Make sure the power is switched off.
  2. Remove the case off the microwave if you haven’t already.
  3. Locate the magnetron and use a multimeter to test it out.
  4. The test should show resistance of between 2-3 ohms. If not, you’ll need to replace it.
  5. If that test is fine, then test the metal casing by placing one of the multimeter probes onto it – if the test displays a zero, then this means the magnetron will have to be replaced.
  6. If you replace the magnetron, then put the microwave back together and test if the problem has been solved.

Thermal Fuse

The thermal fuse helps to ensure your microwave doesn’t overheat, and when it does, it tells the control board to turn the microwave off. To check the fuse, all you need to do is locate it and then check if it has blown. If the fuse has blown, it will need to be replaced. Please note that the fuses are different from the fuses you find in your home fuse box – you’ll have to order the exact type for your make and model of microwave from a specialist retailer.

High Voltage Capacitor and Transformer

These components work side-by-side with the high voltage diode to power the magnetron. If they become faulty, your microwave will not be able to heat. Replacing the high voltage capacitor and transformer is very complex and not worth doing unless you have a high-end model microwave. In most cases, when they become faulty you’ll be able to smell a pungent burnt smell coming from the microwave.

Control Board

If you still haven’t found the cause of the problem, then the final component to check is the control board. As the name suggests, the control board controls every aspect of your microwave. When it becomes faulty, your microwave won’t work – and probably won’t even turn on. Replacing the control board only makes sense if you have a high-end microwave, as it is expensive and difficult to replace. You’re probably better off buying a new one.

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