Thermal Runaway & Temperature drops

Updated 3 months ago ​by Tomáš Chvalina

Thermal Runaway is a safety feature designed to prevent the printer from accidentally catching fire. If your printer's thermistor would somehow dislodge itself, electronic parts would get a lower (incorrect) temperature reading. In an attempt to compensate for the lower temperature, the heater would reach dangerously high temperatures, with the printer potentially becoming a fire hazard. Thermal Runaway prevents that from happening.

Thermal Runaway is configured to shut down the printer when the temperature drops by more than 15°C for more than 45 seconds. If the temperature reading doesn't recover in the set time period, the printer will shut down and display Thermal Runaway error.

All hotend heaters are thoroughly tested, so they can run at 200°C with the print cooling fan at a 100% speed (set in Slic3r Filament - Cooling)To print materials that require higher temperatures, the speed of the fan is decreased. For example, PETG requires 240°C, so the fan runs at 40% of its maximum speed. There's a balance between nozzle temperature and fan speed, because higher temperature filaments set more quickly. 

 How to fix the thermal runaway error:

  1. Check the ambient temperature. Suggested ambient temperature is 20°C or more. Unheated garage in winter might cause thermal runaway as heater doesn't have enough power when the print cooling fan kicks in.
  2. Visually check the thermistor if it is still securely placed in the heater block body.
  3. Check the thermistor cable connector on the back of the X-carriage and make sure it isn't loose. This is only an issue with E3D V6.1 with cartridge thermistor. See below.
  4. In your slicer of choice, check the fan power settings and material temperature. 100% fan speed is compatible only with nozzle temperatures around 200°C when using the V6.1 hotend. See below for more details.
  5. Check the fan shroud for any kind of damage. In some cases, users bent the shroud during assembly or when they were removing the printed object. A damaged or tilted shroud can change the airflow and start cooling the heater block directly. For safety reasons, the heater doesn't have enough power (by design) to compensate for that.

Temperature drops during the print

If you see a drop by 5°C - 10°C when the fan is switched on (especially when the printer transitions from the 1st to the 2nd layer), it's normal. The nozzle temperature should recover rather quickly as the PID regulation kicks in.

E3D V6.1 hotend update

You can easily recognise the E3D V6.1 by its cartridge thermistor.

E3D Sock - During the testing, we didn't find the E3D sock to be very good, as it tends to fall off. That can cause print failures and even damage the printer. Failed prints can get stuck to the nozzle and break it. However, if you want to test them anyway, we do have them in stock and we can add it for free to your next order - just leave a note.

Thermal Runaway caused by a connector issue

The thermistor's connector can become loose over time, so first of all, try reseating it. If it doesn't help, it usually means that the small thermistor wires have broken off inside the connector. Your best bet is to cut away the connectors completely, connect the wires directly and solder them together. Our manufacturing process is being adjusted (as of 11th October, 2016), so new printers will be shipped with an updated thermistor wiring.

Temperature graph with loose thermistor connector before and after the fix

Thermal runaway because of print PLA print settings. We were increasing the print temperature to 215°C to make the print stick better to the PEI but failed to set the proper temps of 200-205°C for the later layers. This was not a problem on printers with old V6 heater block. But new heater block version is bigger and therefore has bigger surface area to get cooled by the print fan. Please adjust the "Other layers" to 200°C as on the screenshot. This will be adjusted in the drivers 1.7.5 drivers.

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