OctoPrint is telling my printer to do wrong things



OctoPrint can only talk to your printer over its serial interface, and it can only tell it to do things that you tell OctoPrint to do. So if your printer is doing wonky stuff, its most probably not because OctoPrint is telling it to do that.

Wrong temperatures are set

OctoPrint sends temperature commands to the printer in exactly three cases: When you set a temperature on the temperature tab, when OctoPrint sends GCODE to the printer (e.g. a file to be printed or a GCODE Script) or when a plugin you have installed instructs OctoPrint to send a temperature command to your printer. If you notice that your printer is set to wrong temperatures, check your slicer profile, your configured GCODE scripts, any plugins your might have installed (if in doubt, run in safe mode) and make sure you didn't accidentally set a temperature offset on the temperature tab.

The printer doesn't hold the temperature

That's a problem with your printer or the firmware of your printer. OctoPrint only sends a temperature set command (for when, see the previous section), it's your printer's job to correctly process that. If you see wild fluctuations in your temperature values, check your PID settings.

OctoPrint caused my printer's hotend to overheat!

OctoPrint doesn't tell your printer to go to temperatures that you didn't specify yourself, and it most definitely doesn't do that on its own. It's your responsibility to make sure you configure your slicer profiles so they don't set the hotend to 1000°C. Also make sure your firmware properly detects overheating and that your hotend's temperature probe and heater are properly secured.

OctoPrint made my printer move funny!

OctoPrint does not send move commands on its own. It only sends move commands that you either trigger yourself through the control panel or through streamed GCODE files, or that are triggered by any plugins you might have installed (if in doubt, run in safe mode). It's your printer's job to correctly interpret the received move commands, not OctoPrint's.

OctoPrint crashed my printer's head into the bed!

OctoPrint expects your firmware to take care of not driving the nozzle through the print bed when it sends it a home command - that is the job of your firmware. Make sure your endstops are wired correctly and that your firmware doesn't ignore them or the software endstops.

Print nozzle MELTING my prints!
Prints initiated via Octoprint - see HE heating to 220C