Why Is My LG Microwave Not Heating?

LG wins awards for its appliances’ reliability, but no brand is impervious to issues and LG microwaves can develop problems just like any other. However, if your LG microwave is not heating, it’s not always an issue with the appliance; it could also be a user error.

Nonetheless, a microwave not heating is still a microwave not heating. The result is the same: an inability to reheat last night’s leftover pizza and having to let things defrost naturally, at a painfully slow rate.

This article goes through all the possible reasons why your LG microwave is not heating, helping you solve this frustrating problem and get things back working again.

A quick note on safety

It’s important to know that microwaves have a component inside called the high-voltage capacitor. This component can hold a lethal charge, even when the microwave is disconnected from power.

Therefore, microwaves should ideally be repaired by a trained professional. However, if you do plan to repair your microwave yourself, it’s essential to first learn how to safely discharge the capacitor.

Why your LG microwave is not heating

Now that you understand the safety risks involved with microwave repairs, let’s dive into the likely reasons your LG microwave is not heating.

Wrong settings

You’ve likely already checked this, but it can sometimes be overlooked. If your LG microwave is set to the lowest power level or defrost mode, your food and beverages won’t heat sufficiently, no matter how long you leave them inside.

Broken magnetron

The magnetron is the main heat-producing component in a microwave. It generates the electromagnetic waves (microwaves) that penetrate your food and heat it. Simply put, if the magnetron stops working, your food and beverages won’t heat up, even though the microwave will still run.

Unfortunately, you cannot repair a broken magnetron, and they’re not cheap to replace either. That means you’ll need to consider whether replacing the magnetron is worth it, or if you’re better off buying a new microwave.

To confirm the magnetron is faulty, you’d need to disassemble the microwave, remove the magnetron, and test it with a multimeter.

Door switch issue

Microwaves are equipped with several door switches, also called interlock switches, which ensure the microwave won’t heat when the door is open. This is an excellent safety feature, but if you have an issue with one of the door switches, the microwave won’t heat, even when the door is shut.

LG microwaves normally have three or four interlock switches. To determine if any are broken, you will need to inspect the door latches or hooks to see if they are bent or snapped and test the switches with a multimeter.

Blown high-voltage diode

The diode enables the microwave to generate the high voltage required to power the magnetron, which heats the food. It does this by converting AC power to DC power, which is necessary for the magnetron to function.

Due to gradual wear over time or power surges, the high-voltage diode can blow. When this happens, the microwave will likely still run, but it will stop heating. Like the magnetron, a blown diode cannot be repaired and must be replaced.

You would need to disassemble the microwave, remove the diode, and test it with a multimeter to confirm if it’s faulty.

Faulty high-voltage capacitor

The high-voltage capacitor stores electrical energy and releases it in pulses, boosting the voltage. It works hand in hand with the high-voltage diode, making the conversion of AC power to DC power possible, which is necessary for the magnetron to function.

If the high-voltage capacitor malfunctions, your LG microwave likely won’t heat, and it will need to be replaced. However, remember that the capacitor stores a lethal charge, so attempting to replace it yourself can be extremely dangerous unless you know how to safely discharge it. Consider hiring a professional technician for safe replacement.

Problem with the high-voltage transformer

The high-voltage transformer steps up the power from the standard voltage (120V) to the higher voltage (2,000 to 3,000 volts) needed for the magnetron to operate. If you notice a burning smell coming from your microwave, it could indicate that the transformer has burnt out.

Once the high-voltage transformer fails, your LG microwave will stop heating, and the transformer will need to be replaced. Testing and replacing the transformer is quite complex, so it’s best handled by a professional.

Blown thermal fuse

The thermal fuse is a safety device that prevents your microwave from overheating. It does this by cutting off power when a certain temperature is reached. However, once the thermal fuse is triggered (also known as ‘blown’), your microwave will no longer heat until the fuse is replaced.

You cannot repair a thermal fuse, so replacing it is the only option. To test and replace the thermal fuse, you will need to disassemble your microwave, remove the thermal fuse, test it with a multimeter, and replace it if it doesn’t have continuity.

An issue with the main control board

The control board is the brain of your LG microwave and may cause it to stop heating if it begins to malfunction. Diagnosing issues with the control board is complex, especially if there are no obvious signs of damage or burning and should be handled by a professional.

Additionally, the control board is one of the more expensive components to replace, so you’ll need to consider whether it’s worth doing or if buying a new microwave is a better option. This decision depends on the age of your appliance, as it’s generally not cost-effective to do expensive repairs on microwaves that are over 7 years old.