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Whirlpool Microwave Not Heating? Here’s Why (+ How To Fix)

A Whirlpool microwave not heating isn’t always a severe issue because a few inadvertent errors could prevent the appliance from working. However, if the cause is a broken part, you must detect the faulty component and repair or replace it. So, why is your Whirlpool microwave not heating?

Here’s why your Whirlpool microwave is not heating:

  • There’s an electrical problem.
  • The user settings are wrong.
  • A door switch is not working.
  • Cooling or ventilation is poor.
  • A fuse or thermostat is blown.
  • The diode or capacitor is bad.
  • The transformer is burned out.
  • The control board is defective.
  • The magnetron is not working.

These problems are not listed in any order, nor is any issue statistically likelier than the rest. So, you have to inspect one component at a time based on your suspicions and accordingly fix the problem. Keep reading to investigate all the reasons for a Whirlpool microwave not heating.  

There’s an Electrical Problem

Many household Whirlpool microwaves require a 120V power source with up to 20A current. If the cord is damaged to the extent that it affects the voltage or reduces the amperage, it may prevent the microwave from heating, albeit the low-power display might work. 

Some models require a 240V circuit, so the voltage and amperage change accordingly. Also, a few Whirlpool microwaves, like the over the range models, demand a dedicated circuit. Thus, an issue related to the power supply, whether voltage or amperage, can affect the heating function. 

Like all microwaves, Whirlpool’s models have high-voltage capacitors, diodes, and transformers, all of which fire up the magnetron. A substantial voltage or amperage fluctuation could prevent the magnetron from emitting the microwaves necessary to induce the required heating effect.

A Whirlpool microwave’s terminal block or noise filter board could also be a problem, especially if there’s no voltage or amperage issue in the circuit. 

Whirlpool microwaves that are over the range or hood combo models have a noise filter board with electrical terminals, a fuse, etc. If this board is broken, your microwave won’t work. In some cases, the microwave may turn on but not heat. You’ll have to inspect this board, too.

Some Whirlpool microwaves have a conventional terminal block with three terminals with two live ones. If this block is broken or any live terminal is burnt, corroded, etc., then the connection won’t work as it should. Such an issue is likely in Whirlpool microwaves running on 240V.

If a 120V microwave has a dead live wire terminal, you won’t have a working display or control panel. However, a 240V microwave has 2 x 120V legs, so one live wire terminal working will still power the display, but not the magnetron to emit microwaves and the oven to heat as a result. 

How To Fix

You can inspect the power cord for visible signs of damage, such as burns, tears, cracks, etc. A damaged power cord needs to be replaced. If the power cord looks alright, measure the voltage at the wall receptacle and the terminals inside your Whirlpool microwave. 

If you find low voltage at the wall outlet, you must consult an electrician because the circuit isn’t alright. If the receptacle has the required voltage, you can test the same at the legs on the terminal block or noise filter board of your Whirlpool microwave oven.

If there’s no problem with the receptacle and power cord, then you must test the terminals in the microwave. This part may be a block or a noise filter board with three terminals, subject to the microwave model. You must replace a broken terminal block or noise filter board.

The User Settings Are Wrong

A Whirlpool microwave not heating could be due to a few user settings or modes, including:

  • Demo mode
  • Low power
  • Clock / timer

If any operation that was programmed is still running, your Whirlpool microwave may not run. These issues could be inadvertent, so you have to review your settings and the modes you have selected. 

How To Fix

Check if you have selected the microwave timer to cook. Sometimes, users rely on the clock or timer, which isn’t the cooking mode. The clock shows standard time, not a cooking duration. And it doesn’t regulate the microwave’s heating. 

Similarly, your Whirlpool microwave may be in demo mode. You have to turn this off for the microwave to heat up. The specific process depends on the model. 

Here are the steps to turn off demo mode on some over the range Whirlpool microwaves:

  1. Keep the microwave plugged in and powered.
  2. Open the door, press 3 on the keypad, and hold it for 5 seconds.
  3. Once you see the ‘d’ icon flash on display, press start in 5 seconds.
  4. If the demo mode is on, it will be turned off, and you’ll see ‘dOff’ on display.
  5. If the demo mode is off, you’ll see ‘dOn’ on display, so repeat the steps to revert.

Some Whirlpool microwaves display the feature as Store Demo Mode, which is the same. Also, a few models provide access to this mode through the Clock button. So, you open the door and press the button a number of times until you see ‘Demo’ on the display panel and press start.  

Here’s a video about how you can access the demo mode on some Whirlpool microwaves: 

If the clock and demo modes aren’t a problem, you should check the power level. The power level is essentially a cooking program for your Whirlpool microwave. Many models have a power level down to 0%, which means your microwave won’t heat. 

Press the Power pad after you set the microwave to heat to check the level. If the power level is not what you want, increase it to the desired percentage. You can change the heating power in 10% increments or decrements. 

A Door Switch Is Not Working

Whirlpool microwaves won’t heat if the door is not completely closed. An open or improperly sealed door won’t activate the switches inside the microwave, and the magnetron won’t work. Always inspect the door and ensure it is closed and sealed. If it is, then inspect the door switches.

How To Fix

Some Whirlpool microwaves have a packaging spacer attached to the door. You should remove this and close the door completely. If you have an old microwave, check the trim and if the door is perfectly aligned. A misaligned door won’t close properly. 

You may also have faulty latches. The latches are mechanical parts, including the springs. These fixtures aren’t the switches. The switches are inside the microwave, behind the user interface or control panel that you access.

Most Whirlpool microwaves have 2 or more door switches. You must test the continuity of these switches to know if they are working. If any switch is defective, you must replace it. 

Cooling or Ventilation Is Poor

Whirlpool microwaves require adequate ventilation. The electronic components should also be cool for the appliance to function properly. The ventilation is facilitated by the blower, while the cooling fan takes care of the control board and other electronic components. 

If your Whirlpool microwave doesn’t have sufficient ventilation and cooling, it may not heat and can shut abruptly. You may also have a blown fuse or tripped thermoprotector. This problem is more prevalent for countertop microwaves because the hood combo models work differently.  

How To Fix

Here are the inspections and standard remedies for cooling and ventilation issues:

  • Ensure your Whirlpool microwave is on a steady and level countertop or surface.
  • Provide around 30 cm (~12 inches) of space above a countertop Whirlpool microwave.
  • Keep some space on all sides of the microwave, including the space behind and under.
  • Check if the cooling fan for the electronic control board is working or if its motor is bad.
  • Replace a bad cooling fan motor if it is broken or check the thermoprotector for this part.
  • Get a new thermoprotector for the cooling fan if it is blown and doesn’t have continuity.
  • Inspect the line and thermal fuses, along with the other thermoprotectors, if any is blown. 

A Fuse or Thermostat Is Blown

Whirlpool microwaves have several fuses and thermistors or thermostats, including:

  • Line fuse
  • Thermal fuse
  • Cooling fan fuse
  • Hood fan thermistor
  • Cavity thermostat
  • Forced convection thermistor
  • Magnetron hi-limit thermostat 

Every blown fuse or broken thermistor disables the associated component, hence function. So, you have to inspect each of these fuses based on your preliminary suspicions and findings. If one of the fuses, thermistors, or thermostats has failed, you have to replace it.  

How To Fix

You have to test all these fuses or thermistors for continuity. You can also check some of these thermostats for resistance. However, you must disassemble the Whirlpool microwave to access these parts. Refer to your manual or schematics to locate the fuses, thermistors, or thermostats.

Here are the tests you need to conduct:

  • Unplug the Whirlpool microwave and take it apart.
  • Don’t access the capacitor unless you discharge it safely.
  • Remove the wires from the terminals of all the fuses or thermistors.
  • Use a multimeter to test every fuse or thermostat for continuity.
  • A working fuse or thermistor should pass the continuity test.
  • Also, you can perform a resistance test for some of the thermistors.
  • A hood fan thermistor should read around 10K ohms at room temperature.
  • A forced convection thermistor should have around 17K ohms of resistance.

The Diode or Capacitor Is Bad

All Whirlpool microwaves have a high-voltage diode and capacitor, whether it is a countertop or an over the range model. If either the diode or the capacitor fails, your microwave won’t heat. I don’t recommend testing these components unless you have insulated pliers, screwdrivers, etc.

You should also check these components only after you have tested the parts I have discussed until now. If you notice a burnt component inside a Whirlpool microwave after you take it apart, that should be the first part to inspect. 

How To Fix

Here’s how must approach testing and fixing a diode or capacitor in a Whirlpool microwave:

  • Unplug the Whirlpool microwave and let the capacitor discharge overnight.
  • Otherwise, you must use a resistor or insulated pliers to discharge the capacitor.
  • Exercise caution if you use insulated screwdrivers to discharge, as there’ll be a spark.
  • Don’t access the diode or capacitor before you discharge the latter to avert a shock.
  • If you want to test only the diode, take its wires off the terminals using insulated pliers.
  • Use a multimeter to test the diode for continuity and replace it if it fails the test.
  • Similarly, test the capacitor’s continuity and if it has a short to decide whether it is bad.
  • Ideally, you should remove the capacitor from the microwave before testing its continuity.
  • To test for a short, use your multimeter probes on a terminal and the capacitor’s chassis.

The Transformer Is Burned Out

A burned out transformer won’t let your Whirlpool microwave heat. So, you have to inspect the transformer for a fault. A visual inspection can help if there are signs of charring or burned parts. Otherwise, you have to inspect the continuity of all the windings on the microwave transformer.  

How To Fix

Here’s how you can test a Whirlpool microwave’s transformer:

  1. Unplug the microwave and remove the housing and panels to take it apart.
  2. Locate the transformer and remove the wires from its terminals.
  3. Unscrew the mounting or securing plate to take out the transformer.
  4. Get a multimeter to test the resistance of all three windings.
  5. The primary winding should have around 0.5 ohms of resistance.
  6. The secondary winding should read approximately 120 ohms.
  7. The filament winding should have ~0 ohms of resistance.
  8. Also, test the resistance of the windings to the grounding.
  9. The primary winding to grounding should read infinite resistance.
  10. Likewise, the filament winding to grounding should be an open loop.
  11. If the windings don’t have continuity or resistance, the transformer is burned out.
  12. Also, if any windings and grounding have continuity, the transformer is bad. 

The Control Board Is Defective

A defective control board can be the cause of your Whirlpool microwave not heating. Otherwise, you have a bad magnetron. You can inspect both, but there isn’t a simple electrical test to check if a control board is fine. You can look for burnt or charred signs to suspect the control board.

How To Fix

Generally, Whirlpool microwave control boards are beyond repair. So, you need a replacement. I recommend checking everything else, including the wirings and harnesses or connectors. If you find nothing wrong in the unit, the control board is probably the culprit, and you need a new one.

The Magnetron Is Not Working

The magnetron in Whirlpool microwaves is unlikely to fail without a severe triggering factor. Yet, you may have a magnetron that is no longer working. You can suspect power surges or excess energy reflected to the magnetron. Nonetheless, you cannot repair or fix a bad magnetron. 

How To Fix

Test the magnetron’s continuity and resistance. Here are the normal readings:

  • The two terminals of the magnetron should have continuity after removing the wires.
  • The resistance between the two terminals of the magnetron should be less than 1 ohm.
  • If the terminals don’t have continuity or the expected resistance, replace the magnetron.
  • Either terminal should not have any continuity with the chassis or the magnetron’s case.
  • If the terminal and case have continuity or nominal resistance, replace the magnetron.

Author

  • Chris Hewitt

    Chris is a Texas-based freelance writer who loves the outdoors and working in his garage. When he's not enjoying the Texas sun, he can be found tinkering with all sorts of things in his workshop.

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