How to Test a Thermal Fuse

Thermal fuses serve as crucial safety devices in many appliances and electronic equipment, protecting them from overheating and potential fire hazards. However, like any component, thermal fuses can also experience faults or failures over time.

How to Test a Thermal Fuse

Knowing how to test a thermal fuse is essential for troubleshooting and ensuring the proper functioning of your appliances. In this article, we will explore the step-by-step process of testing a thermal fuse.

By following these guidelines, you can determine whether the thermal fuse is the cause of any appliance malfunction and take appropriate measures for repair or replacement. Whether you are a DIY enthusiast or simply want to understand the inner workings of your appliances, this guide will equip you with the knowledge and techniques to effectively test a thermal fuse.

How Do I Know If My Thermal Fuse Is Bad?

Your appliance is not working properly, and you suspect that the thermal fuse may be to blame. You’ll need to check it for signs of failure. To do this, you’ll need a multimeter.

First, unplug your appliance from the power source. Carefully remove the back panel of the appliance until you can locate the thermal fuse. It should have two terminals on either end with a wire connected to each one.

Unplug Your Appliance From the Power Source

Using your multimeter, set it to ohms (Ω). With one probe touching each terminal of the fuse, take a reading on the display screen. If it reads “infinite resistance,” which means there’s no current flowing through it, then your thermal fuse has failed and needs to be replaced.

If the thermal fuse has not failed, the reading you get should be between 0 and 1 ohm. Anything more than 1 ohm is an indication that it has a low resistance, which could indicate that it’s on its way out soon and should be replaced as a preventative measure.

Once you’ve determined whether or not your thermal fuse needs to be replaced, make sure to properly dispose of the old one and install a new one before turning on your appliance to ensure safety and proper operation.

Depending on your appliance model, replacing a thermal fuse can sometimes require extra steps, like removing other components in order to access it. If you’re unsure if you can handle this yourself, it may be best to consult a professional for assistance.

Can I Bypass a Thermal Fuse?

No, it is not recommended to bypass a thermal fuse. Doing so could put your appliance at risk of overheating and causing further damage to the appliance or causing a fire hazard. Thermal fuses are designed to cut power when the temperature reaches unsafe levels, so bypassing the fuse could be dangerous.

Bypass a Thermal Fuse

If your thermal fuse is not working correctly, it should be replaced, and bypassing the fuse eliminates this safety mechanism. If you are uncertain why the fuse has tripped, it is best to consult an appliance repair technician for diagnosis and repair.

It is possible to test the thermal fuse without bypassing it. To test a thermal fuse, first disconnect the power from the appliance and locate the thermal fuse. Touch each of the leads with an ohmmeter and check for continuity; if there is no continuity, then the thermal fuse is bad and should be replaced.

Testing your thermal fuse regularly can help ensure that it is working correctly and prevent potential damage to your appliance or fire hazards caused by a faulty thermal fuse. Be sure to always follow safety guidelines when working with electrical appliances and never bypass the thermal fuse.

The safety of you and your appliance should be a priority; it is better to replace the thermal fuse than attempt to bypass it. It may cost you less in the long run if you ensure that your thermal fuses are tested and replaced as needed.

10 Methods How to Test a Thermal Fuse

1. Visual Inspection

Start by visually inspecting the thermal fuse for any signs of physical damage or discoloration. Look for burn marks, melted parts, or broken connections. If any visible issues are found, the thermal fuse may need to be replaced.

Visually Inspecting the Thermal Fuse

Though a visual inspection is not always enough to indicate if the thermal fuse is still functional, it may be able to spot some problems that would otherwise go unnoticed.

2. Resistance Test

Disconnect the power source from the appliance and use a multimeter set to the resistance (ohms) mode. Touch the multimeter probes to the thermal fuse’s terminals and check the resistance reading. A properly functioning thermal fuse should have very low resistance, typically close to zero ohms.

If the resistance reading is high, it indicates a bad thermal fuse. Replace with a new one if this is the case. Resistance tests should be used with caution and if possible, a qualified technician should be consulted.

3. Continuity Test

Similar to the resistance test, use a multimeter set to the continuity mode. Connect the multimeter probes to the thermal fuse terminals and check for a continuous tone or a “closed circuit” indication. If there is no continuity, it suggests a faulty thermal fuse that needs replacement.

When conducting a continuity test using a multimeter, check the device settings as they may vary according to the manufacturer. Also, ensure that the thermal fuse is properly connected to the device, as it can also affect continuity.

4. Temperature Test

Heat the thermal fuse using a heat gun or hairdryer, gradually increasing the temperature. Continuously monitor the fuse’s temperature using a thermometer and compare it to the thermal rating specified by the manufacturer. If the fuse does not trip or cut off the circuit within the specified temperature range, it may be faulty.

5. Bypass Test

Disconnect the power source and carefully bypass the thermal fuse by connecting the electrical wires directly. Restore power to the appliance and monitor its operation. If the appliance functions normally without any safety concerns or overheating issues, it indicates a faulty thermal fuse that requires replacement.

To ensure the safety of your appliance, always use a thermal fuse that has the same specifications. Never bypass the thermal fuse permanently.

6. Voltage Test

Connect the thermal fuse to a power source and use a voltmeter to measure the voltage across its terminals. Ensure that the voltage matches the specifications provided by the manufacturer. A significant deviation from the expected voltage range may indicate a faulty thermal fuse.

Connect the Thermal Fuse to a Power Source

7. Resistance to Heat Test

Place the thermal fuse in an oven or a controlled heat source. Gradually increase the temperature and monitor the resistance readings using a multimeter. Compare the readings to the manufacturer’s specifications to determine if the thermal fuse operates within the expected range.

If the resistance readings vary drastically, then the thermal fuse is likely faulty and needs to be replaced. Take note that this process should only be done by trained technicians as it poses a risk of damage to the thermal fuse.

8. Professional Thermal Imaging

Consult a professional technician who can use thermal imaging equipment to analyze the thermal fuse’s performance. This method can provide detailed visual information about heat distribution and potential anomalies in the thermal fuse’s operation.

Thermal imaging can also reveal hot and cold spots around the thermal fuse, indicating faulty connections or damage to the device. Professional thermal imaging requires expensive equipment that must be by a licensed technician, so it can be expensive.

9. Comparative Test

If possible, compare the resistance or continuity readings of the thermal fuse in question with a known good thermal fuse of the same model. This method helps identify any significant deviations or discrepancies between the tested fuse and the reference fuse.

If the readings show a significant difference, it is likely that the fuse has failed and needs to be replaced. However, if the readings are within acceptable parameters, then the fuse may be functioning correctly and unlikely to be causing any problems.

10. Manufacturer’s Data Analysis

Consult the manufacturer’s documentation, including datasheets or technical specifications, to understand the thermal fuse’s design, operating characteristics, and testing methods recommended by the manufacturer.

This information may include the fuse’s temperature rating, current rating, time-current curves, and fault-clearance times. The manufacturer’s testing methods should be followed, as these are designed to accurately test the fuse.


Testing a thermal fuse is an effective and easy way to ensure that your appliances are running safely and efficiently. The important thing is to follow the steps above and be sure to replace any components that are no longer functioning properly.

If you choose to replace the fuse yourself, make sure you obtain the right parts for your appliance model and ask a professional if needed. Finally, testing your thermal fuse should become a regularly scheduled practice in order to ensure your safety and extend the life of your appliance.

Taking these steps will demonstrate that you take pride in your appliances as well as protect them from potential damage.  Now that you have all the information on how to test a thermal fuse, why don’t you give it a try?

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Enrique Howard

Hi, I am Enrique. I started my professional life as a handyman and did a lot of external and internal repair of home and office with a little bit of electric and plumbing support. I have extensive experience in tools testing such as drilling, turning, milling, and non-conventional machining like EDM. So let me help you on your journey towards becoming an enlightened DIYer with amazing tools that you can use on your project.

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