Why is my Microwave not Heating? We've got you covered.

Written by David Lewis
6 Min read
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Table of contents

Microwaves are a fantastic bit of technology that we truly take for granted, and when they begin to have a couple of faults, it can be a really big problem for us.

They give us quick dinners, popcorn, cooking or just heating food and have a lot of different uses.

But when they break, what can we do?

Check all of your Basics First

Whilst it sounds obvious, it's really easy to forget some of the simple things that you may have forgotten that can be problems. Make sure to check all of the settings and the timer so that everything is what you're aiming for and that it is all set up for you to have a nicely cooked meal.

It is also possible that you are trying to heat something that can't be heated, microwaves work by heating the water inside of the food to cook it rather than the actual food, so make sure to check the meal you're cooking is microwaveable.

When doing tests for a broken microwave, just use water to start and build from there so that you can figure out the problems.

Little Disclaimer

Reading through this article, or any others like it, will not make you an expert on microwaves and electronics, they should help to figure out the problem, if it's something serious and you're in danger then make sure to get a professional to help.

Calling a Professional

As said before, if you are unsure of what the problem is and you don't even know where to start, bring in a professional to have a look at the problem. Microwaves aren't simple machines at all, they're difficult to wrap your head around and so don't hesitate to bring someone else in.

Make sure you're really confident about any of the repairs that you're doing before you begin.

How does a Microwave actually work?

Beginning to understand how a microwave works is the first thing to do when you want to start wrapping your head around repairing something yourself. Wikipedia tells us that all of the key ingredients of a microwave are:

  1. Some kind of high voltage power source or power converter
  2. A high voltage capacitor that connects to the chassis.
  3. An important part called the cavity magnetron that essentially turns power into microwave radiation
  4. A magnetron control circuit
  5. A waveguide
  6. The cooking chamber, made of metal
  7. A turntable to rest the food on that will slowly rotate
  8. A control panel

Microwaves started with the thought process of an American scientist who noticed that a chocolate bar had melted in his pocket that had his radio equipment in.

Since then these have changed the game for kitchens all around the world, and are a really important part of modern households, and they aren't even too difficult for you or me to understand.

The magnetron is the heart of the microwave, and it's what produces the high-frequency radio waves. These waves are pushed into the metal box that you place your food in and make the water inside the food vibrate so quickly that it creates heat, then cooking the food!

Why is it not heating?

As with any other piece of modern technology, the best way to sort out the problem is to single out each component and figure out what part is faulty.

Door Switches

A super simple little piece of the microwave that can cause some really big problems without you even noticing. If the door switch isn't operating right and the door isn't closed fully then the microwave won't even allow itself to start. Microwaves can be harmful to us with the door open so it's really important that they don't start with the door open.

A simple little check for this is that the light should go on when you open the door, and then off again when closed. So, if the door is closed and it's still got the light open, there's a problem with the door switch and it needs to be fixed.

Slamming the door shut isn't going to be the fix that you think that it is, close it firmly and check again, and if its a mechanical button then check that it isn't stuck or something like that.

If neither of these things works, the most likely answer is that the door switch is broken and will need to be replaced or fixed. It's more than likely that this kind of repair will have to be handed over to a professional.

The High Voltage Diode

What this little part does is convert the A/C energy into D/C energy for the microwave to use, you'll know if there's a malfunction with this as it will usually make a humming or buzzing noise.

If you have a close look at this it'll be pretty obvious that it's burnt out as it should look pretty obvious. Diodes will just deteriorate over time and it's a pretty common occurrence, luckily, however, it's a cheap and easy part to replace.

You can use a multimeter to test these, and you should see a high resistance on one side and a lower resistance on the other, so if it's consistent throughout, you know it needs to be replaced. It's a part that will only cost about $20 and you shouldn't spend any more than that.

Magnetron

Magnetrons use an insane amount of power, it's an essential part of the microwave and is basically what heats your food, any kind of malfunction will blow the fuse pretty quickly.

You'll have to pull out the multimeter again for this test, and you need to look for a resistance of 2-3 ohms. If it does then move a probe onto the metal casing, if it's giving you a reading, it's not the problem, but if it says zero then this is probably the issue.

If it's a blown fuse then replacing the fuse alone won't fix the issue, there will be another underlying issue that will cause the same problem again. A new magnetron is possible to install, but it's a tricky piece of work that will require a professional to install.

Thermal Fuse / Thermal Protector

Any appliance in your home that heats will have some kind of overheating protection, and when these go, the fuses will more than likely have blown and will need replacing. Fuses aren't anything particularly difficult, but they're harder to find than regular fuses, so that might take a little bit of investigation. Your best bet is to try the manufacturer.

Transformer / High Voltage Capacitor

These are some of the more complex parts to fix, they work alongside the diode to supply power to the magnetron. Because they are so complex and difficult to replace, you are better off getting a new microwave unless you have a very expensive, modern microwave.

You'll know it's the transformer because the microwave will start to give off a horrible smell.

Control Board

It's a little self-explanatory but without the control board, you won't have any control at all over your microwave, it's the brain of the machine.

Along with the transformer, this is one of those parts that is so difficult to replace, you might be better off just replacing the microwave depending on how expensive it was.

It's also an easy thing to know what is wrong as you will probably lose all control over the machine, and it'll be surprised if it even turns on.

Conclusion

Microwaves are an amazing and revolutionary piece of kit that have certain parts that are easy to repair and other parts that are certainly not. Now you can hopefully know what those parts are and begin to make an informed decision on the next step, but remember to always be careful and make sure that if something seems dangerous, call in a professional.

How do you fix a microwave that doesn't heat?

The way to begin fixing a microwave is to diagnose it by each piece to figure out what is wrong, and how to fix it will depend on the piece that's faulty. Remember to also check all of your basics so that no mistakes are stopping the microwave from working properly.

Is it worth fixing a microwave that won't heat?

If your capacitor or control panel has gone then you should only fix it if it's a high end, expensive microwave. These parts are too expensive to fix and are extremely complicated, usually taking a professional to fix. This will just be down to each person individually.

Why is my microwave running but not heating?

There is most likely a problem with the magnetron, a complicated part to fix that will require a professional to repair more times than not. It is also possible that the food you're putting in isn't microwaveable as it needs to have water in for the microwave to work.

Appliances made simple. 

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