Lulzbot Mini Hot End Temperature Fluctuations at High Temperatures

I seems to be seeing some odd temperature fluctuations but only at higher temperatures (>240C). This occurs with the machine sitting still, the Hot End off and the part cooling fans off as well. It almost seems like the thermistor table is wrong, however, I checked the firmware and the correct profile is selected for firmware version 1.8.3. Is anyone experiencing similar issues? This doesn’t occur at lower temperatures (<200C).

If you have access to a digital multimeter you can check the resistance settings on the tool head to see if the thermistor or heater cartridge is bad. With the printer turned off and unplugged, disconnect the hot end from the wiring harness and test hot end for the proper resistance. The smaller black and red wires coming from hot end itself are for the thermistor and should read ~100k ohms at room temperature. You can locate these two wires on the 20 pin connector which connects the tool head to the harness from the printer. It will be the two pins on the outside, separated from the other pins. The larger red wires are connected to the heater cartridge and should read ~20 ohms. The large red wires will be visible at the 20 pin connector.

Also you mentioned firmware version 1.8.3 and I wanted to check on that, the most current version of Cura runs with firmware version so if you are using firmware version it would probably be a good idea to update to the most current version of Cura and flash for that firmware as it will be the most stable and have all the current bug fixes enacted. You can download the most current Cura here:
On the download page that you will be directed to when you select your OS there will be guides for uninstalling the old version of Cura, as well as clearing your computers cache, be sure to complete both of these steps before updating to the newest Cura to allow a clean install of the new software. Then follow the prompts at start up in Cura to add a new printer profile and flash your firmware.