In both of the C2 & R2 printers, there is a PID wizard for calibrating the feedback loop of the Marlin firmware. This wizard should be ran 4 - 6 times in a row. Why? The values are best guesstimates for loop control of the hot-end temperature. As such, they can be too loose for controlling the temperature. You need to write down the finishing values for each pass. The best set of control values will be the point where all 3 of the values have a minimal difference from the previous calibration. Example with a new hot-end: PID Initial: 26.34, 1.93, 90.1 1st Pass: 25.08, 2.22, 70.88; Difference of 1.22 & 0.29 & -19.22 2nd Pass: 24.99, 2.09, 74.72: Difference of 0.07 & 0.13 & 3.84 3rd Pass: 23.03, 1.93, 68.86: Difference of 1.96 & 0.16 & 5.9 4th Pass: 23.26, 1.89, 71.46 (Final pass) Difference of -0.2 & 0.04 & -2.6 Each value P, I, D influence the other two values, so you need to find the point where the values don't change by much ( as shown in the above example ).