It is great to be able to load up a plate of leftovers and just toss it in the microwave for a few minutes. You are given hot delicious food without having to turn on your oven again to make it. Unfortunately, if your food comes out still pretty cold or not even a little bit warm at all, your microwave is failing in pretty much its only function.
While you definitely want to get to the bottom of why your microwave is no longer heating food, you will want to take a few things into consideration. The first issue is that microwaves, even when unplugged, can hold a dangerous charge in the high voltage diode. It is something that you can touch accidentally when investigating, and needs to be discharged for your safety first. As such, you may want to consider professional repair when your microwave has a problem instead of a DIY approach.
It is also worth considering that a cheap $20 microwave you have had since college may be more cost effective to just replace. This is particularly true if you are set on doing the repair yourself. Sometimes a microwave isn’t worth the headache or the cost of the replacement parts.
If you are still set on finding out why your microwave is no longer heating food, the following causes might be responsible.
Faulty Door Switches
If your microwave still seems to work, but when you press the start button, nothing happens, the cause could be a door switch. In order to keep microwave users safe, the appliance comes with several door switches. If these switches are not activated when the door is closed, then the microwave will not run.
You can test these switch with a multimeter and usually replace them pretty safely with only minimal disassembly.
The magnetron is the part in your microwave that actually produces the heat. As such, if it is no longer functioning correctly, then it will not efficiently heat your food. Unfortunately, replacement magnetrons are typically expensive and really quite complex to replace. Furthermore, it requires you to work in that aforementioned dangerous high voltage area.
Faulty High Voltage Diode
The high voltage diode and capacitor on your microwave supply power to the magnetron. As such, if the diode has gone faulty, it may not be powering up the part that actually produces the heat. This can be confused with a faulty magnetron, which can be a costly mistake if you buy the wrong part. To be sure, you will want to check the diode, capacitor, and magnetron with a multimeter. Although, if the diode has burnt out, you will be able to see visible scorching on it.
It is crucial to remember that the high voltage diode and capacitor can hold a high charge. Even if you suspect it is faulty, you will first want to discharge the stored power or contact a professional to investigate further.
Microwaves can be very dangerous to work on and we recommend calling a professional the minute you need to open the cabinet to work on it. Only someone with experience should attempt to fix a microwave that is not heating.