The answer to 'zone control system blowing hot air' is that there are several common causes, including issues with the thermostat, damper motors, or the control board. Symptoms can include some zones getting hot air while others are cool, or the system blowing hot air even when cooling is needed.
Some DIY troubleshooting steps include checking the thermostat settings, inspecting the damper motors, and testing the control board. However, if the issue persists or you're not comfortable working on the system, it's best to call a professional HVAC technician to diagnose and repair the problem.