During four decades of dealing with hydronic systems, I’ve confirmed two characteristics that always govern their operation. Both are rooted in the tenants of thermodynamics. Neither should be thought of as mysterious. When understood and respected, these behaviors unfailingly reveal why a given system does what it does. This knowledge can be a real asset for designing as well as troubleshooting hydronic systems.
Fundamentally, there are two things that every hydronic system you’ll ever design, install or troubleshoot “tries” to do. They all try to operate at conditions in which energy input equals energy output. This applies to both mechanical and thermal energy inputs and outputs. I call these states thermal equilibrium and hydraulic equilibrium.