The answer to 'why is my zone control system blowing hot air' is that there could be several common causes, such as a malfunctioning thermostat, a problem with the zone dampers, or an issue with the HVAC unit itself. Symptoms may include inconsistent temperatures, the system not responding to zone control settings, or the system blowing hot air even when it's set to cool.
Some potential solutions include checking the thermostat batteries and settings, inspecting the zone dampers for proper operation, and ensuring the HVAC unit is functioning correctly. However, troubleshooting and repairing a zone control system can be complex, so it's often best to call a professional HVAC technician, especially if you're not comfortable working with the system.