What the F3T4 error means on a Whirlpool microwave and how to fix it yourself (2024)

Has your Whirlpool microwave suddenly started displaying an F3T4 error code? This usually indicates an issue with the magnetron thermistor that can prevent the microwave from heating properly.

But don’t worry – you can often resolve this error code yourself and get your microwave heating again in no time. Let’s walk through the process for diagnosing and clearing an F3T4 Whirlpool microwave error code.

If you find out that you need any replacement parts for your Whirlpool microwave 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 in this article is based on general service manuals and 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.

What does the F3T4 error code mean?

Whirlpool microwave ovens use a magnetron thermistor as one of several thermal protectors to monitor temperatures and prevent overheating. Mounted directly on the magnetron tube, the magnetron thermistor allows the microwave’s control board to monitor the temperature of the magnetron as the microwave is cooking food.

If the thermistor senses that the magnetron has exceeded a temperature of 125°C, it signals to the control board to shut off the microwave to prevent tube damage. An F3T4 error will then appear on the display panel.

Until the magnetron cools and the thermistor resets, the F3T4 code will continue displaying and the microwave won’t heat. This is most commonly caused by a faulty thermistor that incorrectly reports high temperatures, but a wiring or control board problem can also produce the error.

Read more: How To Use A Multimeter To Check Appliance Parts

Safety precautions

Microwaves contain high-voltage parts and can 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.
• 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.
• With the microwave unplugged, remove the outer case to gain internal access.
• Wear insulated gloves and use insulated tools when testing any parts.
• Check all parts for damage before reassembling and powering up the microwave again.
• If the appliance has recently been used, give it plenty of time to cool down before working on it.
• Take your time while working to prevent accidents and personal injuries. Rushing is the enemy of precision.
• Work in a well-lit area so you can see and access appliance parts.
• Keep your workspace free of clutter and other obstacles. Keep children and pets away from the work area.
• Check the user manual to see if there are specific installation or safety instructions related to your appliance or replacement part.
• Be gentle when handling or removing parts. Excessive force might damage the appliance or cause personal injury.
• 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.
• Always take photos or make a note of wiring terminals or other connections before disconnecting them to make reassembly easier.
• Don’t test live voltage with a multimeter if you’re unfamiliar with how to prevent short-circuiting.

Read more:

How to troubleshoot the F3T4 error code

Follow these steps to clear the F3T4 error from your Whirlpool microwave.

Step 1: Discharge the 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.

Step 2: Check the thermistor connection

1. Make sure the microwave is unplugged from the power outlet.
2. Find the magnetron thermistor, which is typically near the magnetron tube.
3. Inspect the connection point of the magnetron thermistor. Look for any signs of damage, corrosion, or loose connections. If it’s damaged, replace it.
4. If everything looks OK so far, set a multimeter to resistance mode (Ω) and use the probes to measure the thermistor’s electrical resistance at room temperature.
5. Check the meter reading against the specified resistance range in your microwave’s user manual. The thermistor should read around 10kΩ at room temperature.

If the thermistor is out of the acceptable resistance range, it will need to be replaced.

If the resistance is normal, then you’ll need to replace the relay control board.

Read more: How to Clean a Microwave

More information

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

If you have any other appliance repair needs or projects, don’t hesitate to explore our thousands of free videos and troubleshooting guides. If you need replacement parts or some extra help, grab your model number and head over to AppliancePartsPros.com, where you can chat with a pro, order parts, read our DIY blog, and more.

Be sure to subscribe to us on YouTube and follow us on Facebook, Twitter, and Instagram!