Open Hydronic system - Legionella Disease

How do I tell if a hydronic heating system is an open system? Is there a specific component I need to be looking for? The attached link are about Legionella disease. I am also including a blurb from the ReportHost software that I use about the potential concern.

A hydronic/domestic hot water (DHW) system was installed, where one water heater appeared to supply hot water for both potable water (drinking, washing and bathing) and for heating interior spaces. This appears to be an “open” system, where a cross connect allows water from the hydronic loop to mix with water from the potable water loop. If not configured so high temperature flushes occur, this type of system can act as an “amplifier” for Legionella bacteria due to stagnant water being at low temperatures in the hydronic loop when the interior space heating system is inactive. This poses a risk for Legionnaires’ disease. Such “open” systems are not allowed in some municipalities due to this risk. Recommend consulting with a qualified hydronic heating specialist to determine if the system is configured to perform high temperature flushes, and/or to discuss alternatives or modifications to this system. For more information, visit: