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Hey all!

I finished re-wiring my Rostock hotend (installed a new cartridge heater and a fresh 100k thermistor. I have a feeling I should re-run the PID auto-tune, but I'm curious - do I need to re-set my Kp, Ki, and Kd numbers in the eeprom before I start the calibration?

Should not have to.

I've done the same without issue and ended up with good results.

You shouldn't need to. Theoretically, if you are using the same heat resister and thermister, the old PID settings should be the same. Factors that may effect this are how you install the new resister and thermister (e.g. wrapping more or less tin foil in the stock hotend will cause a different amount of heat transfer that can possibly change your results) but this change is probably so minimal that it wouldn't matter anyway.