Ender 3 Thermal Runaway (3 Ways to Protect Your 3D Printer)

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Written By: Mario De Lio

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Thermal runaway error message on an ender 3 3d printer

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Ender 3 thermal runaway is the scariest thing to happen during the 3D printing process.

Thermal runaway is a condition where the printer can’t stop heating up. If the 3D printer doesn’t have thermal runaway protection, it can damage the printer or cause a fire.

What is Ender 3 Thermal Runaway

Thermal runaway error message on an ender 3 3d printer

Ender 3 thermal runaway is a condition where the nozzle or bed temperature becomes unregulated and continues increasing temperature until a major failure occurs.

A thermal runaway error is when the printer heats up to an extreme level causing damage to the printer or causing a fire.

Many 3D printers have safety features known as thermal runaway protection to prevent these issues from occurring.

The Ender 3 series is popular because they produce excellent print quality at budget-friendly prices. But Ender 3 printers are not well protected from thermal runaways. 

New Ender 3 printers ship with a thermal runaway protection feature. But older printers may ship with the safety features disabled or may not include any such thermal runaway protection feature.

We’ll look at some safety tips below to help you prevent thermal runaway while printing.

Maintenance and Printer Setup

Close up of the print head on an Ender 3 V2

Thermal runaway is often caused by a deterioration of your printer’s basic electrical and mechanical setup.

The first course of defending your printer from thermal runaway is ensuring your 3D printer is properly assembled and well maintained.

While assembling your Ender 3 3D printer, it’s important to ensure you follow all the steps correctly. Most importantly, you’ll want to double-check the wiring connections.

After you’ve assembled your 3D printer, you must ensure it remains in top condition. It’s important to regularly maintain your 3D printer as part of your precautionary measures.

Regular maintenance can help prevent catastrophic issues caused by thermal runaways and ensures your Ender 3 continues to produce high-quality 3D prints.

3D printers create a lot of vibration during the course of printing.

Over time, the vibrations can loosen screws and electrical connections. Faulty wiring and loosened connections result in poor contact, leading to thermal runaway. 

While performing maintenance on your 3D printer, it’s a good idea to check all of the wiring connections and tighten loose bolts.

Close up of Dario tightening the screws on the Ender 3 heating cartridge and ensureing the thermistor wire is connected

But if you want to prevent thermal runaway, you’ll want to focus your attention on the hot end.

More specifically, ensure the heating cartridge and thermistor are correctly positioned and properly secured.

Securing these components reduces the chance of your thermistor falling out of the heat block.

The thermistor and the heat cartridge must be placed directly in the center of the heat block. Once you have ensured they are correctly positioned, tighten the heat cartridge screw and secure the thermistor screw. 

Double-check that the thermistor screws are not pinching any wires. Pinched wires can result in improper temperature readings, which could lead to thermal runaway. 

Close up of the nozzle, heating cartridge, and thermistor in the print head of an Ender 3

What we don’t want is the thermistor to come loose. If the thermistor falls out of the heat block, it will measure the air temperature, not the nozzle temperature. As a result, your 3D printer’s computer thinks that the nozzle is colder than it needs to be and compensates by increasing the temperature of the already hot heat block.

Bottom Line: Proper 3D printer assembly and regular maintenance go a long way to ensure your Ender 3 runs smoothly. Always ensure that wiring connections are secure and screws are tight for thermal runaway protection. 

Below are several precautionary measures you can take to prevent thermal runaway:

  1. Ensure wiring connections are secure.
  2. Tighten all screws and bolts.
  3. Keep your 3D printer clean.
  4. Ensure the thermistor and the heat cartridge are positioned correctly.
  5. Ensure all the frame and mounting fasteners are tight and aligned properly.
  6. Watch the first layer of every print.



Updating your printer’s firmware is another way to prevent thermal runaway. 3D printer firmware is the “brain” of your machine. Firmware is the software that controls all the motors, sensors, and other components of your Ender 3.

If you’re concerned about thermal runaway, you’ll want to check if your printer’s firmware has thermal runaway protection.

New Ender 3 printers have thermal runaway protection enabled by default.

But that wasn’t always the case.

Older 3D printers may have it disabled or not included at all.

Your 3D printer’s firmware can have thermal runaway protection built into it. I say may because depending on how old your printer is or where you got it from, this function may be enabled or disabled. 

By following the steps below, you can check if your Ender 3 has thermal runaway protection:

  1. Turn your printer on, but don’t preheat the nozzle or print bed.
  2. Unscrew the thermistor wire from the heat block using a screwdriver.
  3. Carefully remove the thermistor wires from the heat block using pliers or tweezers and let the thermistor hang freely away from the heat block. 
  4. Set your printer’s nozzle temperature to 200°C or your standard printing temperature.
  5. Wait about one minute.
  6. Your printer should display a “thermal runaway error” on the screen and should halt heating the printer nozzle.

If your printer displays the error message and stops heating, it means you’re Ender 3 has built-in thermal runaway protection enabled.

After one minute, if the printer does not display an error message and the nozzle temperature keeps increasing,

Wait for your printer to cool down before reassembling the transistor cables. Be careful not to touch any hot components, as it can cause a burn.

If your Ender 3 doesn’t pass the test, you can activate thermal runaway protection in your Ender 3’s existing firmware or update to new firmware with thermal runaway protection. We recommend updating your firmware with built-in thermal runaway protection, such as Marlin firmware.

Fire Safety Tips for 3D Printing

An ender 3 v2 3d printer in a Creality enclosure

When discussing fires and thermal runaways, robust prevention measures are often the best course of action.

But, while the above 3D printing tips can help reduce the chances of printer failure, they can’t reduce the risk entirely.

It’s always good to have backup systems in place.

The following points will introduce ideas to help ensure a fire doesn’t spread if a thermal runaway occurs and leads to a fire. 


Does The Ender 3 Have Thermal Runaway Protection?

All Ender 3 printers being shipped today have thermal runaway protection features in the firmware, but they lack any hardware to prevent or stop the thermal runaway. The firmware on older Ender 3 printers may not have any thermal runaway protection feature.

Is it Safe to Leave an Ender 3 Running Overnight?

Yes, it is generally safe to leave an Ender 3 running overnight. But it is recommended to ensure you print in a fire-safe environment and install firmware with thermal runaway protection.


Mario De Lio

Mario is a Mechanical Engineer with experience working at one of the largest industrial printing companies in the country. He previously owned a rapid prototyping company specializing in designing mechanical parts for 3D printing applications.

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