June 2

How to Repair Microwave Oven Not Heating | Possible Problems and How to Fix Them


Author: Colin Ma
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Kicking things off with a disclaimer - attempting to repair a high voltage microwave oven not heating up or magnetron is inadvisable if you do not consider yourself to be a qualified professional.  You might want to get the pros to perform the repairs you need rather than troubleshooting the problem yourself and risking injury.

Microwaves (see under 300$ ovens here) are high voltage appliances with all manner of dangerous parts - never open the case of an appliance and play around with its components unless you know how exactly you are doing! 

When Your Microwave Stops Working

It’s a scenario many people will be familiar with, which occurs in most households from time to time.  You switch on your microwave (see ovens under 200$ in this post) to heat yesterday’s leftovers, you see the light come on as usual, and it seems to be working fine.

Shortly after, you begin to realize it’s not actually heating the food inside - confirming something is most likely broken.

black oven and microwave

As with most appliances, it’s worth conducting a couple of simple checks before making the decision to replace your microwave (see the new budget-friendly buys). Depending on the model and manufacturer, it could be possible to simply unplug your microwave first, give it a few minutes, and power it up again. This temporary disconnect from the mains could reset any basic issues with a more advanced microwave (for the best stainless steel ovens click here) and may correct the problem.

If you try the above and it still is not working, you most likely have a faulty component under the cover that needs to be replaced or repaired.


Possible Problems and How to Fix Them

If you know what you are doing, most problems with microwaves that fail to heat can be diagnosed with just a few simple tools. These are the five main things you will need to find out what could be the problem with your microwave oven:

  • Multimeter
  • 9-Volt battery
  • Insulated Needle Nose Pliers
  • 2-Insulated Screwdrivers
  • Safety gloves

    Irrespective of where the issue may lie, always ensure you unplug your broken microwave before attempting to repair it. Disconnect it from the mains and remove the residual electrical charge from the capacitor, which can be done by removing the two connectors from the terminals and touching each terminal with the metal part of your needle nose pliers.

    You will see a spark to indicate that it has been discharged - a task that must only be performed while wearing appropriate care of safety gloves. Otherwise, you run the risk of suffering a nasty electric shock.

microwave on top of the oven

Potential Issues with a Door Switch

The average microwave has a series of door switches that prevent the magnetron (which produces the microwave) from switching on and heating items until the door is safely closed.  If even a single switch is broken or stuck in the wrong place, the magnetron will be disabled (even when closed), and your microwave will neither power up nor heat anything inside.

Checking whether or not any door switch is defective is a case of removing each switch one at a time and using a multimeter to assess continuity. If any of the switches you test has a negative response, you can fix or replace it accordingly. This is often the first thing to check as it can be a relatively easy fix before moving on to things like your microwave’s high-voltage diode, magnetron, and so on.

Can You Put a Countertop Microwave in a Cabinet

How to Test the Magnetron

This is the part of the microwave that produces the microwaves needed to heat the food and ingredients inside the appliance. The high voltage diode, high voltage capacitor, and transformer work together to transform AC current to DC, at which point the magnetron is activated, and the heating action of the device is set in motion.

Unfortunately, complex parts like a magnetron cannot be repaired. You can check if this is the cause of the problem by using your multimeter to see if it is functioning. While testing the terminals that lead to the magnetron, you should get a reading of less than 1 ohm. Anything other than this, and you have enough evidence to halt your investigation and order a new component.

part of microwave

That said, it might be even cheaper (and is definitely the easy option) to get yourself a new microwave outright. A typical magnetron can cost anything from $100 to more than $200 - typically around the same price as a basic microwave.

Changing the Fuse

It could also simply be that the fuse in your device needs to be replaced. The manufacturer’s instruction book will provide information on where you can find the fuse box and the type of fuse used in your oven.

Remove the case, search for the fuse and remove it carefully before inspecting it to see if it is broken.  You can then close the case once again, hit the button, and see if the fuse was the issue. It’s not uncommon for a fuse to blow in a microwave - fuse replacement is also one of the easiest of all repairs.

part of microwave

How to Test the High Voltage Capacitor

The process of testing the high voltage capacitor is basically the same as testing the other main components in your microwave. You will first need to remove the terminals from the component before testing them with your multimeter and checking for continuity.

The issues with a capacitor necessitate similar action to that of a failed magnetron. It is a relatively inexpensive part (depending on the model and manufacturer of the device), but it could still be easier to simply pick up a new microwave.

If you know exactly what kind of capacitor you need and how to replace it yourself, you can order one online for a low price.

Testing the High Voltage Transformer

As for the high voltage transformer, it is fairly obvious when this thing fails or begins to blow. These are the components that are responsible for producing a burning smell when the microwave is in use - even if there is nothing inside it at the time.

If you pick up on a burning smell (or any unusual smells at all) while using your microwave, disconnect it from the mains immediately. This is a potentially hazardous component, which, when broken, may trigger a problem far worse than a microwave that doesn't cook food.

Defective Control Board

Last but not least, one of the most complex and sensitive pieces of equipment in most microwaves is its control board. Should it turn out that your control board is the source of the problem, it will need to be replaced - repairing this particular part isn’t usually worth attempting.

In any case, this will typically be the final check carried out after first checking the rest of the more likely components to have malfunctioned. Try the checks above first to see if you can track down the cause of the problem, after which you can assume it is the main control board if everything else seems to be working well enough.

When to Hire Help?

Referring back to the original issue, it is not recommended to begin repairing a microwave (or testing its various terminals) until you are certain you understand how to use the tools properly.

Equipment within a microwave like its high voltage diode, magnetron, and live terminals, in general, can be genuinely hazardous to health. If your microwave is not heating properly and you are not 100% sure what you are doing, it is far better to hire help.

The repairs you need to get your microwave safe, and heating food properly again may be less expensive than you think. In any case, putting a price on your own health and safety is never a good idea - particularly when dealing with potentially hazardous household appliances.

About the author

Colin Ma

An avid home chef, Colin is equally passionate about delicious meals as well as the latest cooking appliances. He's also a keen writer about cooking-related topics.


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