A thermistor is a device that measures and controls the temperature of your 3D printer’s hot end and heated bed. It is a vital component for successful 3D printing, as it ensures that your printer operates at the optimal temperature for your chosen filament.

However, thermistors are also fragile and prone to damage or malfunction. A bad thermistor can cause a variety of problems, such as inaccurate temperature readings, thermal runaway, print errors, and poor print quality.

How to Diagnose a Bad Thermistor on a 3D Printer

There are several ways to check if your thermistor is working properly or not. Here are some of the most common methods:

• Use a multimeter. A multimeter is a device that can measure the resistance of your thermistor. You can use it to compare the resistance value of your thermistor with the expected value from the manufacturer’s specifications or a resistance-temperature table. If the values are significantly different, your thermistor may be faulty.
• Use a diagnostic test. Some 3D printers have built-in diagnostic tests that can check the functionality of your thermistor. You can access these tests from your printer’s menu or software. If the test fails or shows an error code, your thermistor may be faulty.
• Look for symptoms. A bad thermistor can also cause some noticeable symptoms that affect your printing process. Some of these symptoms are:
• Thermal runaway. This is when your printer’s temperature goes out of control and exceeds the safety limit. This can damage your printer or even cause a fire. Thermal runaway can happen if your thermistor is loose, broken, or shorted.
• Higher than usual print temperatures. If your printer requires a higher temperature than the recommended one to extrude your filament, your thermistor may be faulty. This can result in over-extrusion, stringing, oozing, or blobbing.

What to Do About a Bad Thermistor on a 3D Printer

If you suspect that your thermistor is bad, you should replace it as soon as possible.Here are some general guidelines:

• Replacing the thermistor on your hot end:
• Turn off and unplug your printer.
• Wait for the hot end to cool down completely.
• Remove any filament from the extruder.
• Remove any fan shrouds or covers that block access to the hot end.
• Locate the thermistor on the hot end. It is usually a small cylinder with two wires attached to it.
• Carefully disconnect the wires from the thermistor. You may need to cut them or use a screwdriver to loosen them.
• Remove the old thermistor from the hot end. You may need to unscrew it or pull it out gently.
• Insert the new thermistor into the hot end. Make sure it fits snugly and securely.
• Connect the wires from the new thermistor to the wiring on your printer. Make sure they match the polarity and color coding of the old ones.
• Reattach any fan shrouds or covers that you removed earlier.
• Turn on and plug in your printer.
• Calibrate your new thermistor using your printer’s menu or software.