Thermal Runaway Protection for Your Hot End and Heated Bed With Marlin on Ender 3 Pro

Hot end & Heat Bed thermal Runaway

The hot end is and heat bed are the two area of the printer that are heated.  There is a risk of them getting too hot and causing issues.  Ensure you have a modern firmware with thermal runaway protection.  You should already have this if you have a newer version of the Creality firmware, but I'll include some info about it below in case you want to know more.

Thermal runaway protection is meant to detect some kind of issue with one of the heating elements in your printer, and shutting it off so it does not dangerously overheat.

Attached to both your heat bed (the part you print on) and your hot end (the part that filament melts and comes out of) are little temperature sensors called thermistors.  When your printer informs the hot end to heat, the thermistor reports back constantly what the temperature is.  If within a certain period of time, the temperature has not changed as much as would be reasonably expected, your firmware will shut off the hot end as a safety measure.

There are many reasons for thermal runaway protection to kick in, but what they all come down to is the printer is sending commands to the heating element to heat, but the thermistor is not reporting back that it's heating. This can be very dangerous if (for example) your thermistor is faulty, or loose, and the heating element continues to heat while your thermistor doesn't report any change.  Hence, the thermal runaway protection shuts everything off. As long as you have a modern firmware, this should not be an issue: if you are building our own firmware, make sure you know what you are doing when you modify the configuration files to keep this safe.

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