I have been using my 3D printers virtually non-stop since I got them. 3D printing is a fun and exciting way to create new things and one of the questions that I often get asked is how dangerous is a 3D printer and what is the likelihood of it catching fire.
There are very few things on a 3D printer that will cause catastrophic issues and thermal runaway is the leading cause of all fires started by 3D printers.
Thermal runaway on an Ender 3 is the process of the 3D printer elements uncontrollably heating beyond the desired temperature. Thermal runaway can potentially cause damage to the printer and could even result in a fire.
The three components that control the temperature of the hot end are the heating cartridge, thermistor, and heating block.
What Causes Thermal Runaway On A 3D Printer?
- Heating cartridge disconnecting from the heating block.
- Thermistor disconnecting from the heating block.
- Damaged Thermistor Wire.
- Damaged Heating Cartridge Wire.
The main causes for thermal runaway is the heating cartridge disconnecting from the heating block and the thermistor disconnecting from the heating block. Another issue that can cause a thermal runaway error is a damaged thermistor or heating cartridge.
Heating Cartridge Disconnecting From The Heating Block.
The most common cause of 3D printer related housefires is the heating cartridge falling out disconnecting from the heating block. If your printer does not have thermal runaway protection and your heating cartridge becomes disconnected the heating cartridge will begin to heat to its max potential.
At max temperature the heating cartridge will glow red hot and will most likely result in a fire. With thermal runaway protection your 3D printer will be able to identify that the thermistor is reading at room temperature when the heating cartridge is heating up. If the thermistor doesnt read a higher temperature as it should when the heating cartridge is heating the 3D printer will shut down all heating functions.
Thermistor disconnecting from the heating block.
The thermistor disconnecting from the heating block is not as dangerous as the heating cartridge falling out of the heating block but it can still result in a house fire if your heating block cannot withstand the heat of the heating cartridge.
On some occasions the heating cartridge is able to get so hot that it actually melts the heating block and drops the heating cartridge on the build plate which can potentially catch surrounding things on fire.
Most filaments are also flammable (especially PLA) so the heater cartridge falling on a partially completed print will create a fire that is fueled by the filament.
Damaged Thermistor Wire.
A damaged thermistor wire is probably the safest failure on this list because if the thermistor is damaged it will not report a reading back to the printer and the printer will not allow the hot end to heat without a reading from the thermistor.
On an Ender 3 if the thermistor is damaged the easiest way to confirm this is with the hot end temperature reading 0 on the screen. In most cases the thermistor wire is not repairable and will need to be replaced.
Damaged Heating Cartridge Wire.
The counter to the thermistor wire being damaged or broken is the heater cartridge wire being damaged or broken. If the heating cartridge wire is damaged the hot end will not be able to heat up in the first place. The danger comes if the wire is damaged or frayed in the middle of the line which can cause the printer to arc electricity and potentially damage components.
How to Fix Thermal Runaway.
The simplest way to fix thermal runaway is by diagnosing your printer and verifying the thermistor wires and heating cartridge are assembled correctly. If the printer is assembled correctly replace the hot end thermistor wire.
If you are still receiving a thermal runaway message you may need to replace the thermistor wire for the build plate or the heating cartridge.
Thermistor wires are pretty cheap and are an item that is good to have around just in case. I personally have broken a thermistor wire twice on the same printer. The wires are very thin and delicate so please don’t judge.
How To Replace The Hot End Thermistor On An Ender 3.
Step 1 – Remove The Power Cable.
The first step every time you work on your 3D printer is to remove the power cable to ensure that you are safe from the electrical components and also to ensure that any electrostatic discharge damages your 3D printer’s main board.
Your 3D printer’s hot end should be cool when replacing the thermistor.
Step 2 – Remove The Fan Shroud From The Hot End.
Remove the fan shroud from the hot end to access the thermistor cable.
Step 3 – Disconnect The Thermistor From The Hot End.
Remove the screw holding the thermistor wire to the heating block, then disconnect the thermistor.
In this photo the heating block is disconnected from the heatsink. In your case it will not be necessary to remove the heating block from the heatsink.
Step 4 – Remove The Mainboard Cover.
To replace the thermistor in the hot end you will have to remove the mainboard cover by accessing the bottom of your Ender 3 and removing the 3 screws holding the cover on.
Step 5 – Unplug The Thermistor Cable From The Main Board.
Unplug the thermistor cable from the mainboard. The thermistor connection is in the corner of the board as shown below, you might have to remove any adhesion that is added to the board.
Step 6 – Remove The Thermistor Cable.
You can now remove the thermistor cable by pulling the thermistor through the cable cluster from the board end.
Just lightly pull the thermistor cable until it is free from the cable cluster.
Step 7 – Install The New Thermistor Cable.
Install the new thermistor by gently feeding the thermistor through the cable cluster. This can be a difficult and tedious process if done incorrectly but is generally pretty simple and straightforward.
Connect the thermistor to the mainboard in the same slot that you removed the old thermistor from.
Connect the thermistor to the heating block. Do not over tighten the screw that hold the thermistor to the heating block. The thin wires in the thermistor cable are very delicate and can break easily.
Step 8 – Turn On Your Ender 3.
Turn on your Ender 3 to ensure that your thermistor is installed properly. The temperature of your hot end should read room temperature. If the thermistor reads zero on the temperature of the hot end then your thermistor is not installed correctly.
Does The Ender 3 Have Thermal Runaway Protection?
Creality claims that all Ender 3’s are now shipped from the factory with thermal runaway enabled. If you have an Ender 3 that is more than 2 years old you may want to update your firmware to the latest version of marlin, or if you have an Ender 3 V2 you can update to JyersUI.
For directions on updating your Ender 3 firmware please read the linked article that will walk you through the whole process.
How To Test Thermal Runaway Protection On An Ender 3.
The safest way to test thermal runaway protections is by disconnecting the heating cartridge from the motherboard, then heat the hot end.
The thermistor will not heat at all because it is not connected to the main board and after about 1 minute the thermistor should recognize that the hot end is not heating and will throw a thermal runaway error.
DO NOT remove the heating cartridge from the heating block for this test.
The simplest (but not safest) way to test thermal runaway protection is by disconnecting the thermistor from the heating block and then heat the hot end.
If the printer does not throw a thermal runaway error within 2 minutes you should put your printer in cooldown mode and abort the test.
If a thermal runaway error does not show up on your printer within 2 minutes this likely means that your printer does not have thermal runaway protection and you should update your firmware to the latest version available.
Is Min/Max Temp Error The Same As Thermal Runaway?
Min temp error and max temp error are not the same as thermal runaway. In general the three issues are typically caused by a damaged thermistor wire but they manifest themselves in different ways and through different error codes.
Min Temp Error.
Min temp error is a condition where the hot end of your 3D printer is not heating at all and is reading zero on the hot end temperature. This condition typically means that your thermistor is damaged and needs to be replaced.
Max Temp Error.
Max temp error usually occurs as soon as you turn your printer on, the hot end heats up without being prompted and errors out upon reaching max temp.
Max temp error can be caused by a few different components but the most common issue is in the thermistor.
If the thermistor does not fix the issue you likely have a damaged main board which can be much more expensive than the thermistor.