When your microwave stops heating, it can be a frustrating problem to solve by yourself. Not only are you left with cold food and no easy way to heat it, but you also have to figure out how to fix it.
Before you rush out and pay for a technician to perform expensive repairs, you should first read this article. I’ll explain exactly why this problem occurs and show you how to fix it as quickly and easily as possible.
Why is your LG Microwave Not Heating?
One of the biggest challenges when fixing microwave ovens that don’t heat is identifying what exactly is causing the problem. The fact that there are many components inside a microwave also means many potential points of failure.
So let’s first look at what causes this problem so you’ll have a better idea of what needs fixing.
1. There’s a power supply issue
Microwave ovens need a stable and consistent power supply to function properly. So if the power is interrupted or becomes spotty for any reason, your microwave will have trouble getting up to temperature.
This usually comes down to a power surge that tripped the circuit breaker, for example. But in rarer cases, a wall outlet problem may need addressing.
2. Child lock is enabled
The child lock feature on a microwave is a safety button that disables the microwave completely in case any curious young children want to start pressing those buttons.
Sometimes this feature can be activated by accident, or if you use it frequently, you may have forgotten to turn it off.
By disabling the child lock function, we can restore functionality to the microwave.
3. Demo mode is enabled
Most modern microwaves have a ‘demo mode,’ which does not benefit you as a user. It’s supposed to be used by stores when the sales clerk needs to demonstrate the functions of the microwave without actually heating anything.
When demo mode has been switched on (or left on from the store), the buttons and microwave light will still work, but it won’t produce any heat.
So you’ll need to disable demo mode before the microwave heats food again.
4. An error code has been issued
More modern microwaves can communicate to you exactly what’s going wrong with the machine.
This comes in the form of an error code displayed on the front screen; it’s usually an F accompanied by a number.
This error code should be linked up with the description in the manual, which will tell you exactly what needs fixing.
5. An ‘active timer’ has been turned on
Many microwaves have an internal timer that operates independently from the cooking function.
This is supposed to be used when a cooking recipe has instructions to let a particular piece of food stand for X minutes before you need to move on to the next step. The active timer will help you with this by timing it for you.
Sometimes it’s easy to turn this on accidentally and mistake it as the microwave not heating. So you’ll need to disable the active timer and turn the microwave back to the regular cooking function.
6. The door switch isn’t functioning
Microwaves can’t operate when the microwave door is open to protect the user from the harmful radiation that may be emitted.
Because of this, a sensor lets the microwave know when the door is closed and that it’s safe to operate.
If there is a failure in the microwave door switch where it doesn’t fully latch, or it does latch but there is a sensor issue, then the microwave won’t be able to heat.
You’ll need to inspect and fix the door switch before the microwave will work again.
7. The thermal fuse has blown
The thermal fuse is a safety component that continually monitors the internal temperature of the microwave.
Should this temperature exceed the safety threshold, the thermal fuse will blow and immediately sever power to the microwave to protect against fire and prevent further damage to the internal components of the microwave.
These are single-use safety components, so once a thermal fuse blows, the only option is to replace it with a new one.
8. The magnetron has burned out
The magnetron works in conjunction with the diode and HV capacitor to produce the microwaves that heat the food.
Sometimes this magnetron can burn out, usually due to some kind of power spike.
Unfortunately, once a magnetron has burned out, the only solution is to replace it with a new one.
How to fix an LG Microwave Not Heating?
As you can see, most of these problems are simple user errors that can be fixed quite easily by adjusting some easy settings.
In some rarer cases, this problem is caused by a component failure which may need the be addressed by a trained LG technician.
1. Fix the power supply
Without a consistent supply of power, the microwave won’t be able to operate correctly. So we need to ensure that there are no issues with the circuit breaker or outlet.
Start by checking that the microwave is securely plugged into a wall outlet. It’s recommended not to use it on a multiplug or power strip.
Next, you should check the circuit breaker to see if it’s been flipped by something like a power surge. If it has, then flip it back to the ‘on’ position.
Even if the circuit breaker hasn’t been flipped, turning it to the off position and then back on to reset it is usually a good idea at this stage.
If this doesn’t work, there may be an issue with the power outlet itself, and you should try to plug it in elsewhere and see if that allows it to work.
2. Disable the child lock function
When the child lock feature is enabled, the functions on the front control panel will not work. So we need to disable this feature before the microwave is able to heat.
On most LG microwave models, the child lock feature is indicated by an ‘L’ icon on the front display panel. To disable it, you need to press the START/ENTER button and hold it down for 4 seconds.
You should hear an audible beep which confirms the child lock is disabled, and the L icon should disappear from the control panel.
Another way to achieve this is to unplug the microwave for 2-3 minutes to fully power cycle the machine, then when you plug it back in, the child lock feature should be disabled by default.
3. Turn off demo mode.
When demo mode is activated, the microwave might appear like it’s working as the microwave light will still turn on, but the physical ability to heat the food will be prevented.
While you can navigate the complicated menu system to disable this, the easiest way to get a microwave out of demo mode is to unplug it and then plug it back in.
By resetting the appliance, it will usually start up with demo mode disabled.
4. Fix the error code
Depending on which error code you have received and which component it’s referring to will determine which course of action you should take to fix the error.
Here’s a rundown of all the error codes you might receive on an LG Microwave:
- Door – this means the door is open and should be closed.
- F-1 – The thermistor is faulty.
- F-2 – The thermistor has shorted and no heat is being detected.
- F-3 – The internal temperature is not going down due to a thermistor error.
- F-4 – There is an issue with the humidity sensor.
- F-5 – The damper switch has detected a fault.
These types of errors and glitches are most commonly rectified by resetting the microwave. All you need to do is unplug it and wait 30 seconds to let the capacitors fully discharge, then plug it back in.
5. Disable the active timer
When the active timer is enabled, the microwave won’t heat, essentially turning it into a glorified clock.
Fortunately, disabling the active timer is incredibly easy, and all you need to do is press the ‘Timer on/off’ button which will swap the microwave over from timer mode back to cooking mode.
6. Fix the door switch
Microwaves will only heat and cook food when the door is closed, and the sensor is working.
You’ll first need to test the door switch and check whether it’s working. You can do this using a multimeter.
- Start by turning off the power to the LG microwave at the circuit breaker. Wait a few minutes to make sure the capacitors have fully discharged.
- Remove the LG microwave grill and control panel to access the door switch.
- Unscrew the switch assembly to apply the multimeter probes to the switch terminals.
- If it gives you a reading of 0 ohms, then the switch has continuity.
If, however, the switch is not working, it will need to be replaced.
We recommend contacting LG support, who can assist you in sourcing a new switch to install.
7. Replace the thermal fuse
If the thermal fuse has blown, the only solution is to replace it, as these are single-use components.
Once you have sourced a replacement microwave fuse from LG support, here’s how to install it:
- Once again, start by turning the power supply to the microwave oven off at the circuit breaker.
- Remove the front vent and grill that houses the microwave fuse parts.
- Pull the wire and holding screw out of the fuse.
- Pull the old fuse out and discard it.
- Take the new fuse and install it in place of the old one; it should just click into place.
- Install the wires and screws. Then attach the grill and vent.
- Power the microwave oven back up.
8. Replace the microwave magnetron
If the microwave magnetron has failed, the only option is to replace it. As this is quite a complicated process, we recommend contacting LG customer support, who will help arrange for a trained technician to come out and install this component for you.