LG Microwave Not Heating? (here’s why & what to do)

If your microwave isn’t heating, it’s not going to cook your food. There are several reasons why your microwave might not heat, which can range from simple fixes like the child lock or demo mode has been activated. Or something more serious like the thermal fuse has blown or the magnetron has burnt out.

If you own a LG microwave and it’s not heating, keep reading. In this article we take a look at all of the possible reasons why your LG microwave might fail to heat and offer solutions to these issues.

Why Is My LG Microwave Not Heating?

There are a number of reasons why your LG microwave might not be heating which include;

Probable CauseSolution
Incorrect Power level SetEnsure you select the correct level of power 
Demo Mode ActivatedClear the demo mode
Active Timer ActivatedDeactivate the active timer
Door Switch ProblemsEnsure the door is fully closed and the door switches and sensors are working properly
Poor VentilationEnsure the vents are free from any obstructions
Faulty DiodeCheck and replace the diode if necessary
Faulty High Voltage CapacitorCheck and replace if necessary
Faulty TransformerCheck and replace the transformer if necessary
Burnt Out MagnetronCheck and replace the magnetron if necessary
Blown Thermal FuseCheck and replace the thermal fuse if necessary

Let’s take a closer look at each of these issues;

Incorrect Power level Set


Your LG microwave has various power settings. If you have selected an incorrect power setting, the food will not cook. 

Always ensure you have selected the correct power setting sufficient for the food you are cooking.

Demo Mode Activated

If your LG microwave is in demo mode, all of the buttons will work and the noises will sound but the appliance will not heat up. The demo mode is designed to be used in the showroom to demonstrate the functionality of the appliance. It does this without engaging the magnetron.

The easiest way to tell if the demo mode has been activated is to set a cooking time and start the microwave. If the appliance is in demo mode, the timer will run at a much faster rate than usual.

Consult your user manual for the correct way to turn the demo mode off. Once cleared, the microwave should work as normal.

Active Timer Activated

Some LG microwaves have an internal timer that works independently of the cooking functions. It is primarily used when a recipe has instructions to allow the food to stand for a set amount of time before cooking.

The active timer can be set accidentally which will prevent the food from cooking. You will need to disable the active timer to get it to work properly again.

Door Switch Problems

The door on your microwave has to be secure to prevent any of the harmful microwaves from escaping. The appliance will not start to heat food unless the door is fully closed.

You should check the door area for any food particles, dirt or debris that could be stopping the door from closing properly. Then inspect the door latch and strike plate as well as the hinges to make sure they are aligned properly.

If the door is fully closed and everything is aligned as it should be, the problem could lie with the door switches or sensors. This is a job best left to a technician to check.

Poor Ventilation


Your microwave will not operate correctly unless it has adequate ventilation. This is because it could overheat which will cause the appliance to shut down.

You will need to check that the vents are working correctly. Often the vents can get blocked with food or grease which sticks them closed. However, in some cases the vents can become stuck due to wear and tear or old age.

You will need to inspect the vents, clean them and ensure there is adequate space around the microwave to allow sufficient airflow.

Faulty Diode

The diode turns alternating current (AC) into direct current (DC). The AC enters through the transformer and then passes through the diode where it is altered into DC and increased to double its voltage. This is what’s needed to power the magnetron.

If the diode becomes faulty, it will stop any microwaves from being created and your food will not heat up.

As many of the components found inside a microwave are capable of holding onto lethal levels of electricity even when disconnected from the power supply, we recommend getting a technician to investigate and replace the diode if necessary.

Faulty High Voltage Capacitor

The high voltage capacitor works in conjunction with the diode to increase the voltage that enters the microwave to double its original level. This extra voltage is used to power the magnetron.

If the capacitor becomes defective, the magnetron won’t have enough power to produce microwaves and your food will not heat up. This is another job best left to a technician in the interests of safety.

Faulty Transformer

If there is a smell of burning or a loud humming sound when the microwave is working, there’s a strong possibility that the transformer is faulty.

This can lead to electrocution which is why we recommend disconnecting the power supply and contacting a technician immediately. Definitely don’t use the microwave again until it has been checked out professionally.

Burnt Out Magnetron

The magnetron produces the microwaves used to cook your food. If the magnetron becomes burnt out, it will not heat up or cook your food.

Running the microwave with nothing inside the chamber or operating it without the turntable can cause the magnetron to overheat and eventually burn out.

If you suspect the magnetron is the problem, we recommend contacting a technician to check and replace the magnetron for you.

Blown Thermal Fuse

The thermal fuse is a safety device designed to cut the power to the appliance if it overheats. Once the microwave gets beyond a certain predetermined temperature, the thermal fuse will blow to prevent any internal damage.

The thermal fuse on many appliances is easy to replace, but on a microwave, we recommend getting a technician to replace it for you. This is because of the potentially life threatening residual power that can be stored in numerous parts of the microwave including the diode, capacitor and magnetron.

SEE ALSO: Mini Oven Vs Microwave (which to choose)

Frequently Asked Questions

Why is my LG microwave running but not heating?

If your LG microwave is running but not heating it could be because; you have selected the wrong power setting, the demo mode has been activated, the active timer has been set, there is a problem with the door, door switch or door sensors, the vents are blocked, the diode is faulty, the capacitor is faulty, the transformer is faulty, the magnetron is burnt out or the thermal fuse has blown.

How do you reset a LG microwave?

You can reset your LG microwave by disconnecting it from the power supply for 10 to 15 minutes. Once the power is restored, the appliance should be reset.

What does it mean if I can smell burning and hear a humming sound coming from my LG microwave when it is running?

If you can smell burning and hear a humming sound coming from your LG microwave when it’s running, it is likely to be a defective transformer. We recommend getting a technician to investigate and replace the transformer if necessary.

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