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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. However, keep in mind that a microwave can’t get hot on the outside, but repeatedly heating food for long times can shorten the device’s life.
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.
Simple checks you can try before deciding on any repairs or replacements include checking the heating chamber for loose screws or other metal objects and checking to be sure the door is closing properly.
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. This also includes microhood combination microwave ovens.
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 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. This is why it’s good to know what size breaker for a microwave you need. Consider all of these factors when deciding how to deal with a failed capacitor.
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.
Regardless of the cause of the blown fuse, keep in mind that most microwave oven repairs are best done by professionals because of their potential danger, and can cost for replacements or repair can actually exceed that of the cost of a new microwave.
Can I use any 20 amp fuse in my microwave?
No, you can’t use any available 20 amp fuse in your microwave, this could cause damage to various electrical components and potentially be dangerous. You must consult your owner’s manual or the manufacturer’s website to determine the exact type (or types, since many models have multiple fuses) of fuse your microwave uses.
Which fuse usually gets blown in a microwave?
Many microwaves have multiple fuses, but for the most part, the fuse that fails is the main or “line” fuse. If you do want to attempt a replacement, you should consult your owner’s manual to locate the main fuse.
How do I replace the high-voltage capacitor?
A microwave’s capacitor can be replaced by purchasing a replacement (from the manufacturer, usually) and while it can be done by the user, it can be a difficult operation that carries a safety concern due to the chance of serious electrical shock, and is best done by a professional- often a new microwave is the better option.
STAT: A 1000 watt microwave oven will actually use approximately 1700 watts during use. (source)
STAT: The majority of issues with fuses in microwaves are due to failed capacitors. (source)
STAT: Microwave ovens store large amounts of electricity in their capacitor even when unplugged and in general use much more power than most kitchen appliances. (source)