Troubleshooting a microwave that runs but doesn’t heat

Is your microwave not running but not heating? Don’t worry, this is a common problem that you can troubleshoot and fix yourself without the need for a costly service call and we’re here to help!

If you find out that you need any replacement parts for your appliance while you’re troubleshooting, you can enter your model number at AppliancePartsPros.com to order them. Most orders arrive in just two business days, and we have thousands of free guides to show you how to install your new parts.

Important: The troubleshooting information provided in this article may not apply to your specific appliance model. While we strive to offer helpful advice for DIY appliance repairs, variations in models and configurations can lead to differences in troubleshooting steps, error codes and part replacements. For the most accurate guidance, we strongly recommend consulting the technical sheet for your specific appliance model.

Safety precautions

When working on any appliance, remember to keep safety first. Here are some tips to keep in mind:

• Always power off and unplug your appliance or switch off the circuit breaker before attempting any maintenance or replacement work. This keeps you safe by preventing any risk of injury from electric shock.
• Wear insulated work gloves to protect your hands from sharp metal parts, pinching hazards and debris.
• Take your time and don’t rush while working to prevent accidents and personal injuries.
• Work in a well-lit area so you can clearly see and access the interior parts.
• Clear your workspace of clutter and other obstacles. Keep children and pets away from the work area.
• Never work on internal parts with bare wet hands. Make sure the work area is completely dry.
• Check your user manual to see if there are specific installation or safety instructions for your part or appliance.
• Be gentle when handling or removing parts. Excessive force might damage the appliance or cause injury.
• Wear safety glasses when working with chemicals, dust or cleaning large debris to prevent injury.
• If the appliance has recently been used, give it plenty of time for any heating parts to cool down before working on it.
• Take pictures or make a note of wiring terminals or other connections before disconnecting to prevent any problems with reassembly.
• When working with wires, avoid touching any exposed wires or terminals. If you need to touch a wire, use a non-conductive tool or wear insulating gloves to prevent electrical shock.

Read more: How to Install and Replace a Microwave

Microwave safety

Microwaves contain high-voltage parts and have the capacity to store voltage even when they’re disconnected from a power source. Please be very careful while working on a microwave’s internal parts to avoid electrocution, which has the potential to cause serious injuries or death.

• Always unplug the microwave before troubleshooting or making repairs.
• Discharge the high-voltage capacitor before working on high-voltage parts to eliminate the risk of electric shock. Do not continue if you are uncomfortable or unfamiliar with this process.
• Never attempt to run the microwave while its casing is open or when internal parts are exposed. Always completely reassemble the microwave before testing or using it.
• Never attempt to bypass any microwave safety features.
• Never run the microwave empty. Use a glass of water for test running.
• Removing a microwave from over the range is a two person job due to the weight and potential for damage. Follow manufacturer installation instructions for reinstallation over the range after repair.

Read more: How to Clean a Microwave  

Discharging a microwave capacitor 

IMPORTANT: Carefully follow the correct handling and discharge procedures since exposure to the voltage levels inside a microwave can potentially cause severe injury or death. Prioritize safety at all times and follow the instructions and recommendations provided by the manufacturer. If you do not feel comfortable discharging a capacitor, do not attempt to do it yourself.

1. Unplug the microwave from the power source.
2. Grab a screwdriver with good insulation on the handle to protect against electric shock.
3. Gently touch the insulated screwdriver blade to one terminal of the capacitor.
4. Slowly and gently slide the screwdriver forward until it reaches the other terminal of the capacitor. Hold it there for a few seconds. This discharge process often results in a loud and startling ‘POP’ sound.
5. Repeat the process to create a short circuit between each capacitor terminal and the chassis (bare metal mounting plate surface). If the capacitor has three terminals, use the same method.

Troubleshooting steps

Faulty thermal cut-off:

1. Unplug the microwave.
2. Remove the outer casing of the microwave to access the internal parts.
3. Discharge the capacitor before making any repairs or accessing any parts for safety.
4. Locate the thermal cut-off, which is a safety device that disconnects power to the microwave if it overheats.
5. Use a multimeter to test the thermal cut-off for continuity. The thermal cut-off should have continuity when the microwave is at a normal operating temperature.
6. If the thermal cut-off is faulty, replace it with a new one of the same type and rating.

Faulty diode:

1. Locate the diode, which is typically part of the high voltage circuit.
2. Use a multimeter to test the diode for continuity and proper operation. The diode should allow current to flow in one direction but not the other.
3. If the diode is faulty, replace it with a new one of the same type and rating.

Faulty capacitor:

1. Locate the capacitor, which is typically found near the transformer or the high voltage circuit.
2. Use a multimeter to test the capacitor for continuity and capacitance. The capacitor should have the correct capacitance value specified in the manufacturer’s documentation.
3. If the capacitor is faulty, replace it with a new one of the same type and rating.

Faulty high voltage part:

1. Locate the high voltage transformer, which is responsible for generating the high voltage required by the magnetron.
2. Use a multimeter to test the transformer for proper voltage output and continuity.
3. If the transformer is faulty, replace it with a new one of the same type and rating.
4. If the issue persists, the magnetron may be faulty. The magnetron is the component that generates the microwaves and is essential for heating food.
5. Use a multimeter to test the magnetron for proper resistance and continuity. If the magnetron is faulty, it will need to be replaced.
6. Reassemble the microwave and test it to ensure the issue has been resolved.

Read more: 10 reasons why a microwave won’t heat  

Additional information

Thank you for reading! We hope this guide helped you get your microwave working again.

If you have any other appliance repair needs or projects, don’t hesitate to explore our other troubleshooting guides and videos.

If you need replacement parts or some extra help with ordering them, grab your model number and head over to AppliancePartsPros.com, where you can chat with a pro, read our DIY blog and more.

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