Microwave Blows Fuse When Started

If your microwave blows a fuse when started, you most likely have an issue with the microwave oven’s high-voltage capacitor, though there are a few other issues that can cause this to happen. It can happen even to the best microwave oven models, and when it does, your microwave simply won’t heat anything.

Here’s how to check for a problem with the high-voltage capacitor and how to fix it, as well as a few other reasons you might be blowing fuses whenever you turn your microwave on. While you’re here you can also find an answer to other common issues such as food heating unevenly in your microwave.

High-Voltage Capacitor Issues

The high-voltage capacitor in a microwave oven stores large amounts of electricity which gets released to the magnetron (which is actually what produces the microwaves) when the microwave is being used. Because of the high levels of electricity, it stores, the capacitor is designed with a failsafe, regardless of the quality of the model.

If the capacitor malfunctions or becomes defective, it will intentionally blow a fuse when started and not even the internal lights will function. While you can test the capacitor yourself using a multimeter and checking for electrical continuity, it’s often a redundant operation that is also difficult and dangerous for most users.

There are a few reasons why the high-voltage capacitor shorts out or becomes defective.

• If the microwave is new model and the capacitor fails and causes a blown fuse, it’s likely the it was defective when installed, or damaged during transport.
• In an older microwave, the capacitor can fail simply due to wear and tear from normal use. The older the microwave and more it’s used, the more likely this is to happen.
• Lastly, a large surge in electricity- such as one that occurs with a lightning strike- can cause the capacitor to short out

Replacing the High-Voltage Capacitor

If your capacitor has failed, you have the option to replace it, however, that may not be the best option available to you. DIY parts replacement for microwaves can be a dangerous and difficult process because of the large amounts of energy microwaves store even when unplugged, and the need to disassemble and remove major parts such as the microwave cover in order to access most internal components.

Additionally, a replacement capacitor itself can be expensive, and most manufacturers strongly recommend having a professional replace it due to the potential for injury from shock. Since the hourly rate of microwave repair can be anywhere from $70-$150, replacing the capacitor may be more expensive than simply buying a new microwave.

Lastly, a power surge through a circuit breaker that causes a shorted capacitor can (and often does) cause damage to other components, in which case a replacement microwave is almost always the best option. Consider all of these factors when deciding how to deal with a failed capacitor.

Other Possible Causes of a Blown Microwave Fuse

While the capacitor is usually the culprit when it comes to blown fuses, there are a few other issues that can cause a fuse to blow.

• Occasionally a failed cooling fan- either from normal wear and tear, accumulated dust, grease, or some other obstruction- can cause a blown fuse. You may want to check the cooling fan for obvious obstructions before moving forward with other possible replacement or repair options.
• A loose screw or another metal piece inside the microwave could cause a short circuit- you can look inside the heating chamber to see if there’s anything visible. Otherwise, you’d have to open up the microwave’s body, which requires discharging the capacitor first.
• The door interlock switches malfunctioning can cause the microwave to shut down and blow a fuse if the door won’t close properly when in use- this is to prevent microwaves from leaking out while cooking food and is another failsafe. This is another complicated repair/replacement that requires a discharge and is best left to professionals.

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