The temperature control of the two hot ends uses a PID control loop. Seasonal swings in ambient operating temperature as well as changes to the system such as replacing components of the hot end can change the thermal behaviour system as a whole.
In the terminal tab of the user interface, use the G-code command
M303 [Cnn] [Ex] [Snnn] U to run the automated PID tuning process.
[Cnn] where nnn is an integer value denoting the number of heating and cooldown cycles. This should be set to 5 at minimum, however you may increase the cycle count if desired.
[Ex] where x is an index of 0 (T0/left tool) or 1 (T1/right tool)
[Snnn] where nnn is the temperature set point (in ºC) around which to perform the tuning
M500 to save the values once complete.
Running the G-code command
M303 C5 E0 S300 Uwill use 5 heating/cooling cycles to tune the left tool (T0) around 300ºC.
The PID values for low-temperature printing (200ºC - 300ºC for materials such as ABS, nylon, and PC), will be different than for high-temperature printing (300ºC - 450ºC+ for Ultem™, PEEK, and other high performance materials).