How to Replace a Fuse in a Microwave

Is your microwave not running or won’t turn on at all? This is likely due to a blown fuse, which interrupts the power supply to protect the microwave from further issues. In this article we’ll walk you through the steps to test and replace a faulty fuse, along with helping you determine what could be causing this to happen. Replacing a microwave fuse is a simple DIY repair, so long as you pay attention to the important safety precautions. Let’s get your microwave back up and running again!

What is a Microwave Fuse?

The fuses in your microwave are there to prevent damage to the appliance, by cutting off the electricity if either the current or temperature levels are too high. Your microwave will typically have two different types of fuses. The main fuse will be either glass or ceramic, and is used to protect the appliance against overcurrent. The second type is a thermal fuse, which protects against overheating. These fuses are typically one-time use, so once they have blown they will need to be replaced. This is considered a safety feature, as it prevents the microwave from being used when it could cause a fire or further damage to the appliance.

When replacing this part, it’s important to ensure the new fuse is the same amperage as the old one. Checking your model number and purchasing genuine OEM microwave parts will guarantee that the fuse is the correct amperage for your microwave.

Safety Warnings for Microwave Repairs

Microwaves contain a high-voltage capacitor, which can store a lethal amount of electricity. Before beginning any repair work on a microwave, it is crucial that you disconnect the power supply and discharge the capacitor to eliminate any risk of electrical shock. While capacitors will eventually lose charge after the microwave has been unplugged, there is no set “safe” amount of time to pass to guarantee they’re depleted. Manually discharging the capacitor is required to continue safely working on the microwave . If you are not comfortable with performing this task, or do not have the proper equipment, you should contact a repair professional as they will be equipped and trained in properly discharging the capacitor.

How to Discharge a Microwave Capacitor

To safely discharge a microwave capacitor, you will require some shock-proof equipment including rubber work gloves, and insulated screwdriver or pliers. You may also want a copy of the user manual and wiring diagram for your model, so you can easily find where the capacitor is located.

1. Begin by disconnecting the power to your microwave. Unplugging it from the wall is best, but turning off the breaker also works.
2. Next you will need to remove the microwave case. This step will vary depending on the make and model of the microwave, however you will likely need a screwdriver to remove the cabinet.
3. Locate the capacitor in your microwave using your user manual for reference.
4. The capacitor should have two terminals, which you will connect with your tool of choice. It is vital that you are wearing rubber gloves and that the tool you use is insulated. If you are using a screwdriver, lay the metal across both terminals. If you are using pliers, open them and touch each tip to a terminal.
5. Leave the tool across the terminals for a few seconds. When connected, the terminals will likely spark. while scary, it is normal as the capacitor discharges.
6. Remove the tool from the terminals (only touching the insulated end) and you can safely carry on with the fuse testing and replacement.

How to Test a Microwave Fuse for Continuity

If your microwave has a glass fuse, you will be able to tell it’s blown just from a visible inspection. The inside of the tube will be black and burnt, similar to a lightbulb that’s burned out. A ceramic fuse however will need to be tested with a multimeter. Fuses can be found in various places within a microwave, so refer to your owner’s manual for the exact location. Typically you can follow along the power cord to find the fuse holder, but they may also be located along the top, side, or behind the vent grille.

1. Set your multimeter to read for ohms of resistance. If your reader has the option, set it to give you an audible signal. It is a good idea to touch the probes together to hear the sound before testing the fuse itself.
2. Remove the fuse from the holder and place it on a work surface.
3. Place one of the multimeter probes on each terminal of the fuse, and check the multimeter for the reading.
4. If it shows zero ohms of resistance (and makes the beeping tone, if applicable) the fuse has continuity and is still good.
5. If the needle on an analog reader doesn’t move, or the digital display shows anything besides 0, (or does not make a tone), then the fuse has blown and will need to be replaced.

If you don’t have access to a multimeter, you can also test a fuse on any touchscreen device. Hold one end of the fuse between your finger tips, and touch the other end to your cell phone or a tablet or laptop. If the fuse is good, the tip of it should respond on the touchscreen (see if you can type or open an app for example). If the fuse is bad, it usually won’t work on the touchscreen. Please note that while this is a somewhat effective alternative to multimeter testing if you don't own one or it is not functional, testing a fuse with a multimeter will always be the most reliable method.

How to Replace a Fuse in a Microwave

If you’ve determined that the fuse has blown, replacing it simply involves reversing the steps from above.

1. Take your new fuse, and place it into the fuse holder ensuring it is snapped securely in place.
2. Reassemble the microwave and replace the outer cabinet.
3. Plug the microwave back in, and place something inside the microwave (like a cup of water). Do not attempt testing the microwave by running it empty.
4. If the microwave runs and heats up the object, your repair was successful!

Why Does Your Microwave Keep Blowing Fuses?

While a power surge can result in a blown fuses, if you are constantly replacing this part, it can indicate that there are further issues within the microwave. The following parts may be causing this to happen, and should be inspected, cleaned, or replaced if necessary.

Faulty Microwave Door Switches

Door switches are another safety feature found on microwaves to prevent them from running while the door is open. If any of these switches are faulty, it can cause a short circuit which would result in a blown fuse. You can test them with a multimeter for continuity, and replace the door switches if necessary.

Clean Your Microwave Interior

If there is food splatters on the inside walls of your microwave, these could be burning and cause arcing while it is running. Prevent this from being an issue by regularly wiping down your microwave and promptly cleaning up any spills or splatters.

Faulty Microwave Capacitor or High Voltage Diode

These two parts are connected, and either could short circuit and blow the microwave fuse. A capacitor can be tested with a multimeter for continuity (follow the vital safety steps above to discharge the capacitor first). If the diode is faulty, your microwave may have made a loud noise before blowing the fuse. If either the capacitor or diode are faulty or completely failed, they’ll need to be replaced to keep your microwave running properly.

While microwaves are a convenient source to quickly heat up your meals, they are an extremely powerful appliance and safety risks should be taken seriously. If your microwave is constantly blowing fuses, or shows any signs of sparking or overheating, do not continue to use it. If you are comfortable performing further repairs, we have the microwave repair resources to walk you through the steps. Otherwise, your trusted repair expert is just a call away.