Nothing is as disappointing as microwave not heating food but runs. So if you’ve run into this kind of a problem and you don’t know exactly what to do, this guide is for you.
Ideally, your microwave is not heating food but runs because there’s a problem with the door switch, the high-voltage diode might be faulty, or the magnetron may be having a problem. It can also be because a fuse blew or the high voltage capacitor shot.
In this guide, you’ll learn more about why your microwave is not heating food despite running, as well as what you can do to fix the problem.
Let’s get started.
How Does a Microwave Heat Food?
When you slide your pizza into the microwave and close the door, the door switch/sensor engages with the door latch.
The sensor sends the contact signals to the main control board, altering the control that the unit is ready to heat the pizza.
Beyond this point, the high-voltage diode engages with the magnetron, providing it with high power, which it converts into radiation heat to cook your meal.
Why is My Microwave Not Heating Food But Runs?
The following table is a summary of why your microwave is not heating food despite running. It also includes solutions to help you fix the problem:
| Problem | Possible Solution | |
| 1. | Problem with the door switch | You should do a continuity test. Replace the switch with a new one if it doesn’t have continuity. |
| 2. | High-Voltage Diode doesn’t have continuity | Look for visible damages. If there are no damages, test the components for continuity and replace if there’s no continuity. |
| 3. | The magnetron is more than likely faulty | Access the magnetron and test for continuity. Continuity should be zero (0). Replace the magnetron if there’s no continuity. |
| 4. | The microwave’s fuse may have blown | Blow due to overheating. Use a multimeter to test for continuity. Replace the fuses (cavity fuse, thermal fuse, or Thermal protector) if the continuity result is zero. |
| 5. | The capacitor has a problem | Start the fix by discharging the capacitor/transformer. Check for visible damages. If okay, test the capacitor’s resistance rating. Resistance results should be between 2 and 3 ohms. |
1. The Door Switch Has a Problem
Every microwave has a door switch also known as the door sensor. The work of the sensor in the GE, KitchenAid, Whirlpool, Samsung, and LG microwaves is to prevent the magnetron from energizing when you open the unit’s door.
In practice, a microwave will create dead shorts if the door switch closes while the unit is still operating. This happens so that the microwave fuse can blow up and cut off power to the entire appliance.
This simple mechanism is included in every microwave to make sure there’s no time the magnetron will run with the door open.
Unfortunately, this working mechanism doesn’t complete if the door switch has a problem. SO if the switch is faulty, you will have to replace it with a new one.
You can test if your microwave’s door switch is working properly by closing the door. If the lights stay on, it means the door sensor/switch isn’t transferring signals properly.
Consider testing the door sensor for continuity before replacing it.
With the microwave disassembled and the door switch out, set the multimeter sensor to Rx1 and touch the terminals (negative and positive) on the door switch with the multimeter probes.
You should get a zero (0), to confirm continuity, if the switch doesn’t test for zero then it is faulty and you will need to replace it with a new one to get your microwave to heat food again.
To replace the door switch:
- Kill the power and unplug the cord from the socket.
- With a screwdriver, remove the screws holding the grill, and slide and lift the grill to remove.
- Remove the screws holding the control panel and detach the panel.
- With the switch assembly in sight, remove the screws that secure it.
- Push the release tabs to release the old door sensor.
- Disconnect the wire connector to release the door switch.
- Install the new door switch, realign the switch assembly to the frame, and replace the screws to hold it in position.
- Put back the control panel and secure it tightly with screws.
- Fix back the grill and tighten it with screws to secure it.
- Slide the microwave back into the kitchen cabinet and plug the power cord back into the socket.
- Realign the switch assembly to the frame and thread the screws to secure.
- Reposition the control panel, and tighten its screws to hold.
- Fix the grill back and re-thread the screws to secure.
- Open the door and fix the turntable and its support.
With the repair complete plug, the unit is back to power, and the microwave oven should be ready for use.
2. The Unit Has a High-Voltage Diode Problem
The purpose of the diode on your microwave is to double the voltage to nearly 5,000 volts when converting alternating current (AC) to direct current (DC).
It is with this high voltage power that the magnetron can heat the foods.
If the diode is dead, your microwave will not convert alternating current (AC) to direct current (DC). The unit won’t produce the required high-voltage, and, without that power, the magnetron won’t generate the radiation heat necessary to heat food.
First, inspect the diode for visible damages. If there are no visible damages, use a multimeter to test if the part still has its continuous electrical path.
To test for continuity:
- Unplug the microwave cord from power.
- Remove the screws that secure the microwave in the kitchen cabinet, carefully pull the unit and place it on a sturdy surface.
- Unthread the screws that hold the access panel and place the screwdriver across each set of capacitor terminals to discharge.
- Remove the diode. Touch both diode terminals with the multimeter probes. If the diode doesn’t test positive for continuity reverse test the terminals.
If the diode doesn’t test positive for continuity in both directions, it means it has failed and that’s why your appliance is running but not heating.
- In this case, the best solution is to replace the diode with a new one. To do this:
- Disconnect any wire or remove any part that covers the diode.
- The diode has one of its ends connected to the capacitor and the other screwed. Unthread the screw that holds the high-voltage diode.
Note the end that goes to the capacitor before removing the diode so that when installing the new diode, you do it the right way. If you install the diode the wrong way, the microwave will not work.
- Remove the damaged diode ad install the new one.
- Reassemble the microwave, and use the picture taken to ensure you connect everything back to its place.
- Fix the microwave back to the kitchen cabinet and plug the cord back into power.
3. The Magnetron Has a Problem
The magnetron, also known as the resonant cavity magnet, is among the main components of any microwave, as it is the primary method of cooking.
This part of your microwave emits electrons coming from cathodes, which in the process generates electrical energy. The magnetron then produces the radiation heat required to heat your food.
So if you notice that your microwave is not heating food despite running, there is a high chance the magnetron is faulty.
Test the magnetron for continuity if you suspect it to be the reason why your microwave is running but not heating food or drink.
You will need to test the magnetron on your GE, Whirlpool, KitchenAid, Samsung, or LG microwave.
Things are a bit different when testing the magnetron. Instead of testing the magnetron for continuity, we will test its resistance with the help of a multimeter sensor.
- Unplug the microwave power, and disassemble it once it is out of the kitchen cabinet.
- Touch the magnetron with the multimeter probes. You should get a resistance rating of 2 to 3 ohms if everything is okay.
Move one of the multimeter probes onto the metal casing. If you get a reading of zero (0) on the multimeter, something is not right with the magnetron.
Simply replace the magnetron with a new one to fix the problem.
4. The Fuses May Have Blown
If your microwave is running but not heating food, it might be because the thermal fuse, cavity fuse, or thermal protector is faulty.
The thermal fuse, thermal protector, and cavity fuse are available in Whirlpool, LG, KitchenAid, and Samsung microwave. And their work is to turn off power if the units overheat.
- Set your multimeter Rx1 and test each of these fuses for continuity.
- Replace the ones that don’t have continuity.
Note, the Thermal protector, cavity fuse, and thermal fuse do not match the fuses we use in the home fuse box.
They are specific and you will only get them from the manufacturer or an authorized store.
5. There is a Problem with the High-Voltage Capacitor
The high-voltage capacitor, or transformer, helps to condense or keep power. It is from here that electricity originates and goes to the unit’s electrical circuit.
If you know how a battery works then you have an idea of how a microwave’s high-voltage capacitor works.
The only difference is that a capacitor will charge and discharge power so quickly.
There are times when microwave capacitors can short and cause the microwave fuse to blow up. If that happens, your microwave won’t heat food.
The best solution is to replace the capacitor with a new one.
Frequently Asked Questions
1. What Causes the Magnetron to Fail in a Microwave?
A Kitchenaid, GE, Samsung, or LG microwave magnetron may fail because the high-voltage diode is dead. The high-voltage diode supply the magnetron with power to heat your food. So if your microwave’s magnetron failed, replace it with a new one.
2. What are the Signs that a Microwave is Going Bad?
The best way to know your Kitchenaid, Samsung, Whirlpool, or LG microwave is going bad is when it starts releasing less microwaving energy than before. That could also mean you have a magnetron that isn’t working well.
Final Thoughts
Now that you know why your microwave is not heating food but runs, it should be easy to diagnose, fix the problem, reset the microwave, and restore it to optimal performance.