How To Fix A Microwave That Won’t Heat

Technology has brought us this far that whatever we imagine and wish for, comes before us at the click of a button, literally. Take for instance, the simple task of heating up cold food taken out from the refrigerator. Earlier, it’d involve effort to heat it up on a stovetop griddle but not anymore! A revolutionary technology by the name of microwave changed everything.

And the functionality isn’t limited to just reheating; the appliance is widely used for thawing and simple cooking too. The augmented cooking options only explain why life without this convenient gadget could come to a halt. It sure does when your microwave won’t heat! Here, we’ll help you identify the problem before you go on to seek professional help.

If you aren’t familiar with the major components of standard microwaves, convection microwaves and other types, you’re first advised to briefly study about the components, their role and the overall working of a microwave.

1. Failure of High Voltage Diode

If you notice that your microwave runs but doesn’t heat, there could be a problem with its high voltage diode, the component that powers the magnetron so it can heat up the food. The problem arises when this diode, which doubles up the voltage to as much as 5,000 volts to facilitate microwave heating, burns out. As a result, the magnetron fails to receive enough voltage for its proper functioning.

 A problem with the diode can be easily determined because the burnout is visible and prominent, in which case the only solution is to get it immediately replaced by a technician. In case nothing can be determined upon looking at the diode (no visible burnout signs), you can test the diode using a multimeter.

How to Test a High Voltage Diode Using a Multimeter?

how to fix a microwave diode
  1. Make sure you unplug your microwave from the power switch first.
  2. Locate the high voltage diode and remove it to test for continuity. You will first need to remove the cabinet and discharge the high voltage capacitor.
  3. Now set the multimeter to Rx1 and touch the probes to the terminals.
  4. Reverse the probes to check for continuity in the other direction. The multimeter should get a reading that highlights continuity in one direction but not in the other.
  5. If the diode fails to show continuity, or shows continuity in both the directions, you’d need to get it replaced.

2. BrokenDoor Switch

If the microwave door switch breaks, the microwave doesn’t heat despite being switched on. The door switch, also known as interlock switch, is found inside the cabinet and activated with hooks or latches on the door. It helps power several components in the microwave when its door is closed and disrupts power when the door opens. Sometimes due to the failure of the door switch, the magnetron may stop functioning.

How to Test a Door Switch Using a Multimeter?

  1. Unplug the microwave from the power source.
  2. Check whether the door hooks activate the door switch mechanically. If yes, remove the cabinet of the microwave and locate the door switch.
  3. You may need to unmount the microwave if it’s a built in oven and microwave combo, an over-the-range microwave or an under-counter microwave drawer.
  4. Remove it to test for continuity.
  5. Set the multimeter to Rx1.
  6. By lowering the actuator button, touch the probes to the terminals of the switch. The test should give a reading of 0, signalling continuity.
  7. In case it doesn’t match the ‘0’ reading, the door switch would need to be replaced.

3. Broken Magnetron

This is the main part of the microwave that produces heat to cook/warm up the food. If it breaks or stops functioning, a fuse in the microwave might blow out, resulting in the failure of other components. This could be a potential cause why your microwave stopped heating.

How to Test the Magnetron Using a Multimeter?

how to test a microwave magnetron with a multimeter
  1. Disconnect the microwave from its power source.
  2. Remove the microwave’s cabinet to locate the magnetron.
  3. Clean up the microwave cavity if needed
  4. Discharge the high voltage capacitor to ensure that the high voltage diode is working and the mounting bolts are tightened.
  5. In case no other problem is identified, finally remove the magnetron to test it.
  6. Set the multimeter on Rx1.
  7. Touch the probes to the terminals. A reading of 2 to 3 ohms of resistance should be displayed.
  8. Move one probe to touch the metal housing of the magnetron to test if continuity is present.
  9. In case the test indicates that continuity is lost, the magnetron will need to be replaced.

4. Burn out of High Voltage Capacitor

microwave high voltage capacitor

The high voltage capacitor in a microwave works in conjunction with the high voltage diode to convert the transformer’s output to DC voltage, and to double the voltage of the output. Sometimes the capacitor may burn out, resulting in non-functioning of the entire high voltage circuit because of which the ‘microwave not working’ condition arises.

How to Test a High Voltage Capacitor?

A VOM meter with a capacitance-testing ability can help identify the problem, if any. However, remember that the microwave can store deadly amounts of electricity in its high voltage capacitor even after the appliance has been disconnected from the power source.

Therefore, self-replacing any electrical component in the microwave can prove to be fatal at times because of the high-running voltage and its potential to cause electric shock. Always hire a licensed technician to replace the capacitor.

5. Failure of High Voltage Transformer

microwave high voltage transformer

This unit powers the extremely high voltage required to activate the magnetron antenna, which in turn emits the energy used for cooking food in the oven. A failure of the transformer would usually be indicated with an arc and a pungent burning smell.

6. Blow Out of Thermal Fuse

The thermal fuse cuts off power to the microwave in case the latter overheats. You can use a multimeter to determine if the thermal fuse has blown out. If the fuse doesn’t indicate continuity, it needs to be replaced. Note that the fuse cannot be reset, it must be replaced if it has fully blown out. Call a licensed technician to replace it when needed.

Wrapping Up

A microwave has become indispensable to everyday life. Better to restore it to normal functionality in time to avoid grave inconvenience. Follow these simple ways to determine the problem and potentially fix it. If the issue stays unresolved or isn’t listed above, please seek professional assistance to fix it up.

Often times, professional help costs almost the half the money as that of a new appliance. It is hence advisable to get a new microwave altogether, more reliable this time. We’ve compiled a list of the best convection microwaves to help you find a worthy replacement.

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