How to Fix 3D Printer Heating Fail – Thermal Runaway Protection


If you are in the 3D printing field, you might have heard about thermal runaway protection. It definitely stirred up a fuss in the 3D printing community because of its importance and lack of implementation in 3D printers as a safety feature.

This article will guide you on what you need to know about thermal runaway protection.

Thermal runaway protection is a safety feature in your 3D printer which turns the heating systems off if it noticed some kind of fault. If your thermistor is slightly disconnected, it can feed incorrect temperatures to your 3D printer. This has resulted in fires in some cases.

You definitely don’t want to be on the wrong end of thermal runaway protection, so this article will guide you through testing and fixing the thermal runaway feature on your 3D printer.

What is Thermal Runaway Protection and Why Is It Important?

To prevent your 3D printer from thermal runaway problems, the manufacturers have added a safety feature which is known as thermal runaway protection.

This feature is designed to stop the printing process whenever it detects a problem in the printer, especially if the temperature is getting out of control.

This is the best solution to protect your printer, before you start the printing process make sure that this safety feature is activated in the printer’s firmware.

A thermal runaway is one of the most dangerous and frustrating problems that can occur during the printing process. Thermal runaway error is a situation in which the printer can’t maintain the right temperature and may heat up to an extreme level.

Despite all other issues that occur due to this problem, the major threat is that the printer can catch fire which is not so uncommon in this situation.

Basically, thermal runaway protection does not protect the thermal runaway error directly but it aborts the reasons that can cause this problem.

It means that if thermal runaway protection detects that the wrong value of the 3D printer thermistor (temperature reader by detecting the variation in resistance) is being processed for a long time, it will automatically shut down the printing process to avoid damages.

Misalignment or fault in the temperature sensor is one of the basic reasons behind the thermal runway errors.

If the thermistor is not working properly, the printer will keep on increasing the printing temperature to reach the targeted heat and can take the temperature to an extreme level.

This feature will protect your printer from thermal runaway error, the risks of catching fire, and damaging the printer or the people around it.

How Do You Properly Test for Thermal Runaway?

A really simple method shown in the video below is to use a hair dryer on your hotend for a minute or so, to decrease the operating temperature of your nozzle, thereby prompting the ‘Thermal Runaway Printed Halted’ error.

If you don’t have access to a nearby hairdryer, you can do another method.

To do a proper test for the thermal runaway protection feature, you can disconnect the heater element of the hotend or the heated print bed at the time of printing or while sending commands directly to the printer via USB to set a temperature.

You can also disconnect the heater element when the printer is turned off or even if it is heating up.

The disconnecting of the heater element means the nozzle will not be heated. After the temperature testing period and settings specified in the firmware, the printer should stop working and will halt if the thermal protection feature is enabled.

It is recommended to turn off the printer and then reconnect the wires because you may touch the open cables if you try to reconnect the wires while the printer is ON.

When the printer stops working after displaying a thermal runaway error you must restart or reset the printer before starting the printing process.

If the printer keeps on working and does not halt, shut down the printer quickly as it is a clear sign that the thermal runaway protection is not enabled.

How Do You Fix a Thermal Runaway?

There are two possibilities of a thermal runaway error, one is that the thermistor is broken or faulty and the other is the thermal runaway protection not activated.

Below, I will go through how to implement the solution to the issue.

Activating Thermal Runaway Protection

The video below takes you through the process of flashing your 3D printer mainboard to activate thermal runaway protection.

Replace Broken Thermistor

The video below goes through how to replace your thermistor if it is broken.

Before you move forward make sure that your printer is not running and is turned off. Unscrew the fan shroud off to take that out of the way.

Cut down the zip ties that are holding the wires. Now take a small Phillips screwdriver to remove the screw that holds the thermistor at the right place.

Take the broken thermistor out but if it got stuck, it is probably due to the fact that molten plastic is holding the thermistor inside.

If you face such an issue, heat up the hotend to around 185°C as it will melt the plastic, remove that plastic with a tool, then set your hotend to cool down before working with it again.

After the cool down, you should be able to pull out the thermistor gently.

As inserting the new thermistor is a bit difficult, you should put the plug end of the thermistor in the old thermistor wire and fix it with tape. Now pull the exact wire back from the opposite side and you can get the thermistor inserted properly.

Now plug in the new thermistor in the exact spot where the old thermistor was plugged.

Put the zip ties again on the wires and double-check that no wire is open and the thermistor is plugged in properly. Now insert the wires on the other end of the thermistor into the bottom hole and screw them up gently.

The screws should be in the center of the two wires. Now screw up the parts and fan shroud back with the printer.

Methods to Fix Printer Halted Heating Failures

If your nozzle doesn’t manage to reach your desired temperature before giving an error, there are a few reasons for it which  I’ll describe. There are also some pretty simple solutions to accompany these causes.

A usual fix of a halted heating 3D printer is to double-check the assembly of your extruder, making sure there are no large gaps between the heat break, heater block, and nozzle. Ensure your wiring is secure and is put in the correct way round.

A dodgy connection somewhere in your system can definitely be a reason for the ‘HEATING FAILED’ error in your 3D printer, especially if you didn’t properly follow a tutorial or video guide on assembling your 3D printer.

Common connection problems are found in either the heater or temperature sensor of your 3D printer. It can be a good idea to check the resistance of your heater cartridge, making sure it falls close to the specified value.

Some people have had other issues such as a fried mainboard, needing a Power Supply Unit (PSU) replacement, or a hotend replacement.

Since a thermistor sometimes runs underneath screws, they can easily get crushed or come loose, meaning the connection isn’t secure enough to adequately measure the actual temperature of your heater block.

You can get yourself a new thermistor and replace it using the instructions above.

Make sure when you replace your thermistor, you don’t touch either wire to the heater block because it can fry your mainboard.

  • Dialing in your stepper driver voltage can help if they are significantly off
  • Replace your thermistor
  • Use the original mainboard
  • Replace heating element
  • Check that wires aren’t loose on heater block – re-tighten screws if needed
  • Do PID tuning

Does the Ender 3 Have Thermal Runaway?

The Ender 3s that are being shipped now have thermal runaway protection feature enabled.

In the past, it wasn’t always the case, so if you have bought an Ender 3 recently, it will definitely have this feature enabled but if you bought it a while back, follow the steps about to test whether it is active.

It is recommended to follow precautionary measures to avoid this problem. The first thing you should do is the printer’s regular maintenance. Make sure that the printer is assembled correctly, wiring is pretty fine, and the printer is not making any errors.

Make sure that the thermistor is placed in the center of the heat block and is working properly.

Keep the thermal runaway protection feature activated in your firmware but if your Ender 3 is old and it doesn’t have a thermal runaway protection feature in its firmware then you should install other firmware that has the feature activated such as Marlin.

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