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Home /  Appliance Maintenance Home Maintenance / What To Do When Your Microwave Is Not Heating
last_updated_date Last updated: January 7th, 2020

What To Do When Your Microwave Is Not Heating

PUBLISHED: January 6th, 2020 5 MINS READ

Microwave stops heating

Once you own a microwave oven, you can never go back to the days of waiting for food to thaw or stovetop reheating. If you have a convection microwave oven, then you probably do a good amount of your cooking with it. A microwave oven can now even come with a smart display, letting you stream your favorite shows. On the other hand, if your microwave is not heating when switched on, its a downright nightmare.

Before we look at what may be happening when your microwave switches on but refuses to heat up, let’s see what a microwave consists of. These are the parts in a microwave oven’s electronics bay:

  • Magnetron (unless it is an inverter type microwave)
  • Cooling fan
  • Door interlock switches
  • Fuse
  • High Voltage Diode
  • High Voltage Transformer
  • High Voltage Capacitor
  • Controller

How Does a Microwave Oven Heat Food

Microwaves are a form of electromagnetic radiation just as any sort of light is, but with a wavelength that allows them to get absorbed by most food. The magnetron in a microwave oven is what generates the microwaves when the electricity is provided by the transformer. 

The waves then go to the food cavity and are bounced around the chamber. The food molecules are heated up as they absorb the energy carried by the microwaves. The turntable rotates the dish making sure that every part is uniformly heated.

Why Is My Microwave Not Heating?

If your microwave turns on but does not heat up there are a few likely culprits. We have placed them in an order to those needing the simplest to the most complex repair. 

Take great caution when checking on your microwave, because it can store power in the capacitor even when turned off. Ensure that the plug is disconnected and you are wearing rubber-soled shoes and insulation gloves. Discharge the capacitor if you are going to take out the cabinet.

Door Switch

If the door is not properly shut, the oven will not start. So, ensure the door has been shut and locked properly. This sends a signal to the motherboard to allow the power supply.

If the door interlock switches are broken, they will need to be repaired or replaced. The fan and turntable may still work sometimes when a door interlock switch is malfunctioning.

A multimeter will help you figure out if your door switch is working. Remove the back cover of the unit and take out the door switches. The switches should have continuity (which means that there should be functioning electrical connections). Disconnect the switch wires from the oven terminals.

Put the multimeter leads in the continuity mode, on the switches’ wires and check for a beeping tone and a low reading of less than 1. This indicates that the connections are fine. If you do not hear it, this is what will need to be changed.

The latch hooks should also be depressing the switches properly by engaging their actuator. 

Fuse

The fuse may have blown out. Remove the fuse gently and test it for continuity with the multimeter. If the resistance reading is zero then the fuse is fine, else replace it. A blown-out fuse is a common reason for microwave ovens not heating.

High Voltage Diode

This is the component that powers the magnetron. It is absolutely vital to discharge the capacitor if you attempt to test the diode yourself. 

Using your multimeter check what resistance reading the diode displays in both directions. If the diode is functional you will see a higher reading with the leads touching in one direction and a lower reading from reversing the leads. If both readings are low, then the diode is defective.

Capacitor

It is recommended to call your home warranty service provider or a licensed technician if you suspect that the high voltage components like the capacitor or diode are damaged. The capacitor stores a very large amount of electricity and any mishap while handling it will be fatal.

However, the continuity of the capacitor can be checked using the Capacitance Testing Mode of a multimeter if you are an expert. 

Magnetron

magnetron

The magnetron is a vacuum tube with a filament at its center. It is possible for the filament of the magnetron to open, which would result in no heat being produced. 

If upon attaching the magnetron terminal wires to a multimeter, you see a low reading of 2-3 ohms the magnetron may be fine. 

The magnetron should also be tested for continuity between its outer casing and terminals. If there is any, then it needs replacement. There should be no way for the power to get to the outer body of the magnetron.

Any repairs or replacements of a microwave’s magnetron should be handled by a trained professional. Call your original equipment manufacturer as the magnetron may still be covered. If not, your home warranty service provider will help.

If you see any burnt spots or evidence of arcing its likely that the part is the reason your microwave is not heating.

It is also important to keep in mind that these parts may appear fine in isolation. But they might be malfunctioning while the microwave has power running through it. In such cases, it would be safer to have a professional fix your appliance for you.

Microwave ovens can be very durable appliances not needing much repair for several years, especially if they are maintained well. Keeping your microwave clean and covered to prevent any insects from getting in can go a long way. 

Once your original warranty expires, consider getting a home warranty to cover your microwave oven. This will be especially helpful the older it is, as high voltage parts’ replacements can cost quite the tidy sum. If you have an inverter microwave, repairs and replacements will need professional expertise. You can browse the top home warranty providers in the United States to get an overview of your options.

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