PidController arduino

Hello, I am currently working on a heating control project that uses an Arduino board and a motor-controlled valve to regulate the flow of hot water from a primary circuit to a secondary circuit. The primary circuit is connected to a source of hot water (fernwärme/district heating) that maintains a temperature between 60 and 120 degrees, and a permanent pump that can not be controlled or regulated. The secondary circuit is also connected to a constant-speed pump and the goal is to maintain a temperature of about 40 degrees. I have implemented a basic control logic using switch cases and if-else statements, but I am having trouble getting the system to accurately regulate the temperature of the secondary circuit. I have read that using a PID controller can help improve the performance of my system, but I have little experience with this type of control and I need some guidance on how to implement it. I have 4 temperature sensors: Hk_1_TSens_VL (Primary circuit flow) Hk_1_TSens_RL (Primary circuit return) FW_TSens_VL (Fernwärme flow) FW_TSens_RL (Fernwärme return) I would greatly appreciate it if you could help me with the following: • Provide an overview of the steps required to implement a PID controller on an Arduino board. • Help me understand the key parameters that need to be set and how to tune them. • Provide sample code that I can use as a starting point for my project. I am available to provide additional information about my project and answer any questions you may have. Thank you in advance for your help. Best regards, Markus Block