How to Fix a Microwave That Won’t Turn On

It’s impossible to enjoy the splendors of reheated leftovers, warmed-up slices of last night’s pizza, and bags of microwave popcorn if your microwave won’t turn on and run. Fortunately, a microwave that’s not working can often be fixed, sometimes with relatively simple troubleshooting steps.

That’s what we’ll be delving into here: the most likely causes of a microwave not turning on, and most importantly, how to fix these problems to get it functioning properly again.

But before we start, it’s also important to know that fixing a microwave can be dangerous. Therefore, you should ALWAYS:

1. Unplug the microwave before carrying out any repairs.
2. Discharge the high-voltage capacitor to avoid potentially fatal electrocution.

Here’s how to fix a microwave that won’t turn on:

1. Check for power issues

Let’s start with the basics. A microwave obviously needs power to turn on, so it’s worth checking that:

• The microwave is plugged into a functioning outlet that’s switched on.
• Other devices work when plugged into this outlet.
• The circuit breaker hasn’t tripped.

You can also try resetting the circuit breaker by locating the breaker that controls the circuit your microwave runs on, flipping it to the “off” position, waiting 30 seconds, then switching it back on again.

Finally, you can check the power cord for damage, such as splits or cuts in the cord, exposed wires, or bent or loose prongs on the plug. If damaged, the power cord will need replacing.

2. Inspect the door switch

Microwaves won’t turn on while the door is open. This safety feature, controlled by the door switches, ensures no radiation can escape when the microwave is running.

However, if a door switch is defective, it can send an incorrect signal to the control board that the door is open, causing the microwave not to turn on. The door switches are also known as interlock switches because they are activated by hooks or latches on the door that press against the switches when the door is closed.

Here’s how to test the door switches:

1. Unplug the microwave.
2. Check the hooks or latches on the door are not broken or deformed and that the door clicks shut.
3. Remove the microwave’s outer casing by unscrewing the screws that are securing it.
4. Locate the two or three door switches. They are normally near the door latch assembly.
5. Inspect them for visible signs of damage like broken parts or burning.
6. Take a photo of how the wires connect to the door switches to make reassembly easier.
7. Disconnect the wires connected to the door switches.
8. Check the markings on the switches to identify which are “NO” (Normally Open) and “NC” (Normally Closed) switches.
9. Test each door switch one by one using a multimeter that is set to ohms at the Rx1 scale.
10. For “NO” switches, you should get a reading of close to zero ohms when the switch is pressed, and very high resistance or an infinite reading when the switch is not pressed.
11. For “NC” switches, the readings will be reversed.
12. You will need to replace any door switches that fail this test.

3. Examine the ceramic fuse

A microwave will not turn on if its ceramic fuse has blown. The ceramic fuse protects the microwave’s internal components by cutting off power if there is a severe power surge or short circuit. Once it has blown, it must be replaced, since it cannot be reset or repaired.

To check and replace the ceramic fuse, follow these steps:

1. Unplug the microwave.
2. Remove the microwave’s outer casing.
3. Locate the ceramic fuse near the power cord entry point.
4. Remove the fuse and test it with a multimeter set to continuity or ohms.
5. If you hear a beep or get a reading near zero ohms, the ceramic fuse is fine. If you don’t hear a beep or you get an infinite reading, the fuse has blown and needs replacing.
6. Check the markings on the ceramic fuse to determine the correct voltage and current rating, as you must replace it with one with the same specifications.

4. Check the thermal fuse and thermal cutouts

Microwaves use a thermal fuse and thermal cutouts to cut off power to the appliance when it overheats to prevent the risk of fire or damage to components. Thermal fuses need replacing once they’ve blown, whereas thermal cutouts may need replacing if they are faulty.

Many microwaves have one thermal fuse and two thermal cutouts, however, how many they have can vary across different microwave models.

Here’s how to test and replace these safety devices:

1. Unplug the microwave.
2. Remove the microwave’s outer casing.
3. Locate the thermal fuse – it’s usually close to the oven cavity or the magnetron.
4. Disconnect the wires connected to the thermal fuse and remove it.
5. Test the thermal fuse with a multimeter set to ohms.
6. You should get a reading of zero ohms if it’s functioning properly.
7. If not, it has blown and should be replaced with a new thermal fuse.
8. Locate the thermal cutouts – they’re often on or close to the magnetron or the microwave’s cavity.
9. Disconnect the wires connected to the thermal cutouts and remove them.
10. Test each thermal cutout one by one using a multimeter set to ohms.
11. You should get a reading close to 0 ohms (typically between 0 and 2 ohms) if it’s functioning properly.
12. If not, the thermal cutout is faulty and should be replaced with a new one.

5. Hire an expert

If the troubleshooting steps above have not solved the problem, there could be an issue with one of the main components, such as the magnetron, control board, high voltage diode, or capacitor.

These are more complex issues that should be diagnosed and repaired by a professional technician for everyone’s safety.