Ender 3 (Pro/V2/S1) Thermal Runaway: 2 Easy Ways to Solve

Across all of the problems your 3D printer could ever have, thermal runaway is definitely the scariest one. It can cause your 3D printer to light on fire, destroying itself and possibly anything nearby.

Thermal runaway occurs when your printer loses control over the hot end, and it doesn’t stop heating up until it melts itself alive.

While this issue isn’t super common for most 3D printers, it’s been known to happen on some users’ Ender 3 (Pro/V2/S1) printers. And, because of how damaging thermal runaway can be, it’s absolutely vital to take the proper precautionary measures, so it never happens.

This means making sure that your Ender 3 is running a firmware program that has thermal runaway protection turned on. You also should check that the thermistor wire on your Ender 3’s hot end is positioned correctly.

For a more in-depth review of Ender 3 thermal runaway and how you can prevent it on the Ender 3 (Pro/V2/S1), keep reading!

What is Thermal Runaway?

Source: Reddit Posted By Igor000

Thermal runaway is a special and super damaging 3D printing issue where the hot end can’t stop heating up. This causes the hot end to reach super high temperatures, sometimes above 400 °C. At such hot temperatures, the hot end will destroy itself as well as everything that stands in its way. 

As we’ve mentioned, thermal runaway isn’t your everyday 3D printing issue (e.g. under extrusion), but it’s been known to happen on some consumer-grade 3D printers like the Ender 3. This is likely because the manufacturers, such as Creality, don’t always put in 110% effort when designing and assembling the machines.

Note: Creality has stated that the newer V2 and S1 versions have thermal runaway protection built into the firmware. That said, it’s best to check for yourself so there are no surprises.

Why is Thermal Runaway So Dangerous?

Source: Hackaday

Thermal runaway is super dangerous because, on top of destroying the hot end of your 3D printer, it can also cause significant damage to other components on your machine. Just look at the image above! That’s a real person’s 3D printer after a thermal runaway occurred, burning and permanently ruining literally every component on the printer.

That’s hundreds of your hard-earned dollars just flushed down the drain!

But the damage of thermal runaway doesn’t always stop at your 3D printer. In some cases, thermal runaway has caused 3D printers to light on fire and burn its surroundings, like furniture, walls, and more.

So, unless you want your 3D printer to be the reason your house burns down, I’d suggest you keep reading!

What Causes Thermal Runaway on the Ender 3 (Pro/V2/S1)?

Now that you know how dangerous thermal runaway can be, you’ll want to know what causes it. That’s because knowing the causes of thermal runaway will help us determine the right prevention methods for the issue. We’ve gone over the main causes of thermal runaway in the mini-sections below.

Broken Thermistor

Source: Youtube S-Tech

The main cause of thermal runaway on the Ender 3 (Pro/V2/S1), as well as other 3D printers, is almost always a mispositioned thermistor wire.

For reference, the thermistor wire is one of two cables that feed into the hot end assembly, and it’s responsible for telling the motherboard of the printer the temperature of the hot end. The motherboard uses the temperature reading to determine if it should continue to power the heater cartridge, which is the other hot end cable.

When the thermistor wire is mispositioned or over-tightened, it won’t accurately measure the temperature of the hot end, causing the motherboard to continue to send power to the heater cartridge even when it’s already at the right temperature. So then the heater will just continue to heat up until it destroys itself and possibly its surroundings.

Thermal runaway can also happen if the heater cartridge is mispositioned because then the thermistor won’t be able to measure its heat properly. For example, if the heater is not completely inside the hot end’s heater block, it will heat up, but not all of that heat will be detected by the thermistor (which only detects the temperature inside the hot end). This could also cause thermal runaway.

Poor Firmware

Source: Youtube S-Tech

While not a direct cause, thermal runaway can also occur when the Thermal Runaway Protection feature is disabled on the firmware.

This feature is the main way a 3D printer, like the Ender 3, can stop thermal runaway before it causes damage to your printer. And, if it’s turned off or not present in the firmware your Ender 3 is using, then thermal runaway can occur without anything to stop it.

Unfortunately, not all batches of the Ender 3 are shipped out with firmware that has the Thermal Runaway Protection feature activated. We’re not sure why Creality would do this, but it’s been proven by many YouTubers (and myself). It’s mainly a possibility with older versions of the Ender 3, like the original and Pro versions, but it could happen with newer versions too.

How to Fix the Thermal Runaway:

Now that we know what causes thermal runaway on the Ender 3 (Pro/V2/S1), it’s time to get into how you can fix it. And by “fix it”, we really mean preventing thermal runaway because there’s no way to fix the damage caused by this issue. We’ve gone over the best prevention practices in the sections below!

1. Activating Thermal Runaway Protection

Source: Youtube Martin Zeman

The first and most effective prevention practice for thermal runaway on the Ender 3 is turning on the Thermal Runaway Protection feature on your printer’s firmware. This feature is available in most firmware programs, but the best and most reliable option is with Marlin firmware. 

Creality printers, like the Ender 3, already run a Marlin-based firmware program, so this will work perfectly.

What the Thermal Runaway Protection feature does is detect a variance between the thermistor and the heater cartridge. If the motherboard notices that it’s been sending a lot of power to the heater and isn’t seeing much of a change in the thermistor temperature, it will send a thermal runaway error. 

A thermal runaway error will stop all heating on the printer, which is annoying but it’s better to get a thermal runaway error than have a broken printer.

There are two ways you can do this: either go into the existing firmware and activate the feature or install a completely new firmware with the feature already activated. Personally, I recommend going with the latter option because it’s just easier. But if you’re using custom-configured firmware and don’t want to make all of those modifications again, the first option might be easier for you.

Source: Marlin site

To turn on the feature, start by downloading the latest version of Marlin off their website or GitHub page. Make sure you configure it for the Ender 3 (and the specific version of the Ender 3 that you have) by picking out the right configuration files. Then open up the file set in an IDE, like Microsoft VSCode.

In VSCode, find and open the “Configuration.h” file. Then, use the Ctrl-F feature and look for the phrase “Thermal Runaway”. You’ll see a few lines related to thermal runaway protection. Make sure the following three scripts are activated (no “//” in front of them):


And that’s it!

Now just upload the firmware back to your Ender 3. For the V2 and S1 versions of the Ender 3, you can do this via the MicroSD card slot on the printer. And for the original and Pro versions of the printer, you’ll have to use the ISP port on the motherboard, but it shouldn’t be too hard.

2. Repositioning the Thermistor

Source: Youtube FusionSource – 3D Printing

The second main prevention method for thermal runaway is repositioning the thermistor cable.

To do this, start by unscrewing the printhead shroud on your Ender 3. Then locate the heater block on the hot end of your Ender 3, as seen in the image above.

Now, with the printer turned off, remove the silicone sock around the heater block. You should see two sets of cables going into the heater block. The one with the thicker red wires is the heater cartridge; the smaller set of cables (they should be white) is the thermistor.

Use a small Phillips head screwdriver and unscrew the thermistor cable very gently, and then slowly and carefully remove it from the hot end. Give it a good blow of air to make sure it’s clean, and then stick it back in the small hole in the hot end. Now screw it back in just tight enough where it won’t ever fall out, but not tight enough where the wire could be damaged.

And that’s all there is to it! 

Now just turn the printer on and heat it up to your typical printing temperatures, and make sure that it’s displaying the temperature accurately and working.

Other Precautionary Measures

Source: Youtube BV3D: Bryan Vines

While we’ve gone over the main prevention methods for thermal runaway, there are some precautionary measures that you might want to follow. These are good for if your printer does ever run into thermal runaway as these measures will ensure the damage doesn’t go beyond your printer.

Keep A Fire Extinguisher Nearby

Our first precautionary measure is to keep a fire extinguisher nearby. This is a pretty self-explanatory one because if your 3D printer ever runs into thermal runaway, you’ll always have a quick-and-easy way to extinguish the heat.

Some users also like to use a fire extinguisher ball, which is a heat-activated ball that releases fire extinguishing chemicals once it detects too much heat. A good idea for this is to hang it above the print space of your 3D printer because the heat will rise.

Use An External Temperature Sensor

Next, you might want to set up an external temperature sensor. This can be done with a digital sensor or a simple analog one. This is just a good way for you to know the real temperature of the area around your 3D printer so that you can know if the thermistor on your Ender 3 is working properly or not. And then, if it’s not, you can reposition or replace the cable to prevent thermal runaway or stop it in its tracks.

Don’t Place Flammable Materials Nearby

My last precautionary measure for you is to not place any flammable objects nearby your printer. This seems like an obvious one, but some people like to use hairspray, a flammable item, for the bed adhesion on their Ender 3. And in some cases in the past, this has led to thermal runaway causing massive destruction.

Some other items not to keep nearby your Ender 3 include the following:

  • Febreeze (or another scented spray)
  • Wool
  • Furniture with cloth
  • Alcohol (e.g. IPA)


Overall, thermal runaway is an extremely scary issue for 3D printers like the Ender 3 (Pro/V2/S1). But it’s also an issue that can be prevented fairly easily.

The best advice I can give for preventing thermal runaway is to install a new version of Marlin firmware with Thermal Runaway Protection enabled, as well as reposition your thermistor cable. Some other things you can do is keep a fire extinguisher nearby, have a thermometer nearby so you can know how hot your printer is getting, and make sure nothing flammable is nearby your machine.

I hope this helps, and stay safe!

About The Author

Scroll to Top