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Troubleshooting a Commercial Microwave Oven That is Not Heating Properly

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Commercial Microwave ovens are essential equipment in restaurants and cafes for quick and large-scale baking and cooking. So, they must be functional as well to accommodate the requirements of customers. Many technicians receive complaints from restaurants that their microwave oven is running but not heating properly

In this article, you will learn how to fix a microwave when it turns on but does not heat. You will also discover what a commercial microwave oven is and how it differs from a domestic microwave.

Differences Between Commercial & Domestic Microwave Ovens 

Generally, commercial microwaves are different from domestic microwaves in terms of size and power. When it comes to commercial use, the food items require more power and volume than only a commercial microwave can handle. 

Following are the main differences between commercial microwave ovens and domestic microwave ovens:

Spinning Plate – A commercial microwave does not contain spinning plates since it is difficult to rotate large dishes. In the case of a domestic oven, it has a spinning plate at the bottom. 

Material – Commercial microwave ovens are made from stainless steel, making them durable and easy to clean.

Power –  Commercial microwaves operate on 900 to 2200 watts to speed up the cooking process. On the other hand, domestic ovens operate on 700 to 900 watts. 

There are many commercial ovens today that use programmable technology, but still, some restaurants don't use those kinds of ovens; that's why we're not discussing that as a significant difference.

Why is the Microwave Oven Not Heating Things? (3 Major Reasons)

We've enlisted the 3 most common issues and solutions due to which microwaves turn on but do not heat things properly. 

High Voltage Diode 

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If a microwave is not heating up, the most common problem is either a burned-out diode or a malfunctioning diode. A high voltage diode provides power to a magnetron, which is responsible for the proper working of a microwave. 

Testing of a High-voltage Diode

It is best to test a high-voltage diode to determine if there are any problems with it. Here are some simple steps for testing:

  • Unplug the microwave oven.
  • You need to locate the diode and check whether or not it's burnt. If so, it needs to be replaced. Otherwise, further testing is required.  
  • Remove the diode from the microwave oven. 
  • Use a multimeter to run a continuity test on the high-voltage diode. 
  • On running continuity tests, if a multimeter does not show readings, reverse connect multimeter probes to the diode. 
  • The multimeter should show readings in only one direction.
  • You need to replace the diode if the multimeter does not show any reading in both directions or if it shows reading in both directions. 

Door Switch Interlock

An issue with door switches is one of the significant reasons for microwaves running but not heating things. When a microwave closes its door, the door switch operates and allows the microwave to heat. A malfunctioning door switch will prevent the microwave from being activated, so it will not heat. As a consequence, the microwave will often turn on, but it will not heat the object. 

Testing of The Door Switch(es)

  • The first step is to unplug the microwave from the socket for safety assurance. 
  • Locate the door switch wiring and test with the door open and closed.
  • To test continuity, use a multimeter. 
  • While touching multimeter probes with the terminals of the switch, press the actuator button of the door switch. 
  • When a multimeter shows 0 on the screen, the switch is OK; otherwise, you have to replace it.
  • Check for additional door switches.
  • In some cases, the switch is working correctly, but its alignment prevents it from operating correctly.



The Magnetron is the most critical component of a commercial microwave oven. It generates microwave frequency with the help of High voltages and high current DC power responsible for baking or cooking the food. So, if there is an issue with the Magnetron, the microwave will stop heating.  

Testing of the Magnetron

Before testing Magnetron, we recommend discharging the high-voltage capacitor and testing the high voltage diode. If these components are working fine, then proceed to the testing of the Magnetron: 

  • Take out the Magnetron from the Microwave oven, which is not heating correctly. 
  • Connect the multimeter probes to both terminals of Magnetron. The multimeter should show 2 or 3 Ohms on the meter screen. 
  • Now, touch one probe with the Magnetron's body; the multimeter will show continuity. 
  • You must replace the Magnetron if both of the above conditions are not met. 

Note: Before running continuity tests, set the multimeter to Rx1.

Other Issues That May Cause a Microwave to Stop Heating


The capacitor works with the high voltage diode to provide the Magnetron with high voltages and high current DC power. So, if there is an issue with the high-voltage capacitor, the Magnetron will not receive the power to generate microwave frequency. 


Like a capacitor, a transformer is also responsible for voltage or high current DC power transmission towards the Magnetron. So if the transformer malfunctions, the microwave will power up but will not heat. 

Main Control Board

The main control board is an essential component of a microwave oven since it allows every component to work. So, if the mainboard is defective, the microwave will not work correctly. We recommend technicians check all parts of the microwave before replacing the board. Only if all other parts are not faulty, should you consider replacing the main control board.