How To Fix an LG Microwave Not Heating

Microwaves are incredibly convenient appliances. You put in your food, press a couple of buttons, and in a couple of minutes, your food is piping hot and ready to eat. But what can you do if your LG microwave isn’t heating? 

A microwave that won’t heat is pretty much useless, but before you throw in the towel and buy a new appliance, consider these solutions. Our step-by-step instructions walk you through how to fix some common causes of an LG microwave not heating. With a bit of effort, your microwave can be up and running again in no time.

This guide refers to all popular models of LG microwaves, including:

863.5939

ACO1860AS

EM1204S

EM120S

EM3321S

LCRT2010ST

LMH2016ST

LMHM2017ST

LMV1630ST

LMV1680BB

LMV1680ST

LMV1680WW

LMV1683ST

LMV1813ST

LMV2031ST

LMVM2055ST

MA1005W

MA1272MW

MBBS/01

MMV4205AAW

MMV5156AAS

Check your settings

This may sound obvious, but if your microwave is set to one of the lower settings, it won’t heat your food effectively. Check that your LG microwave is set to the highest setting, then try heating your food again to see if the issue is fixed. 

Check the power supply

Make sure that the outlet your microwave is plugged into is working properly. If you’re unsure, unplug the microwave and plug another household appliance into it, such as a lamp or speaker. If the other item works correctly, you can rule out a power supply issue. 

If the other appliance doesn’t work, the circuit breaker that corresponds to your LG microwave has likely been tripped. Here’s how to fix it:

• Locate the electrical panel in your home. If you’re not sure where yours is, check the garage, basement, or storage closet—these are the most common locations for the panel, particularly in older homes. 
• Pinpoint which switch corresponds to the tripped circuit breaker. It will be in the off position, and in some cases, it may be labeled with the area of your home it’s connected to, such as “kitchen.” 
• Ensure the breaker is fully in the off position, then switch it back on to restore the power.
• Run your microwave to check if it’s now heating. 

Reset the microwave

If your microwave has experienced a power surge or other electrical fault, this kind of event can prevent it from heating. Here’s how to reset your microwave and hopefully fix the problem:

• Unplug your microwave from the power outlet. 
• Wait for 10 seconds for the microwave to discharge residual electricity.
• Plug your microwave back in. It will make a beeping sound once it turns on. 
• Press stop/clear to remove any previous settings and restore them to factory settings. 
• Run a test to see if the microwave now heats your food correctly. 

Make sure the door closes properly

For safety reasons, a microwave won’t run unless the door is completely closed. Make sure it’s properly closing, and check to make sure there isn’t anything blocking the latch. 

If your LG microwave is brand new, there might be a shipping spacer still positioned in the door. Make sure to remove this and any other packaging before trying to operate your microwave. If there’s nothing blocking it but the latch still isn’t working, it will need to be replaced. 

How to replace the door latch:

• Ensure the power to your microwave is switched off. 
• Take off the microwave door to get access to the interior. You may need to remove the internal panel first, then the door hinges. 
• Once the door is off, you’ll be able to clearly see the door latch. If it appears broken or worn, you should replace it. Order a compatible replacement part from an appliance parts store. 
• Remove the faulty components and put the new latch in its place. 
• Put the microwave door back together and check to ensure that it’s now latching properly. If it is, run a test cycle to confirm that your microwave can heat your food properly again. 

Important safety note 

While the previous four solutions are fine for a layperson to perform, the following issues require someone who is a certified technician, due to safety issues. Microwaves have a unique feature in that the capacitor stores a huge amount of power even when the microwave is unplugged—enough to cause electric shock or even death. Please don’t attempt the fixes below unless you are qualified. 

Replace the diode

A microwave’s diode powers the magnetron so it can heat the food. If the diode is burned out, your food won’t be able to heat. 

To replace the diode:

• Purchase a new diode compatible with your microwave.
• Unplug your microwave and remove the outer panels.
• Remove the faulty diode from the magnetron, and attach the new one to the capacitor terminal.
• Replace the outer covers, and reconnect all the screws and wiring. 
• Run a test to see if the microwave is now heating correctly.

Replace the magnetron

The magnetron works with the diode to produce microwave frequencies to heat food. If the diode appears fine, the magnetron may be to blame.

To replace the magnetron:

• Unplug the microwave.
• Remove the outer panels, including the bottom panel of the microwave. 
• After discharging the capacitor, detach the magnetron and remove the screws mounting it in place.
• Replace the burned-out magnetron with a new one. You can order a compatible part online from an appliance parts store.
• Put your microwave back together and run a test to see if it’s heating properly.

Replace the thermal fuse

The thermal fuse protects your microwave from power surges and overheating. If your thermal fuse has blown, your LG microwave won’t heat your food—in fact, it won’t run at all. 

To replace the thermal fuse:

• Turn off or unplug the microwave.
• Unscrew the front vent and grill to access the fuse. 
• Carefully remove the fuse. You can test it with a multimeter to ensure it is broken.
• Purchase a new fuse, and install it in place of the blown one. It should click neatly into place.
• Replace the grill and vent.
• Run a test to ensure that the microwave is heating properly.