A popular misconception is that, once all the oxygen in a closed system has been used up, the system will become stable and no more corrosion takes place. Unfortunately, this is not usually the case. Closed Heating and Chilled water systems require an inhibition treatment program to prevent corrosion, deterioration of components and loss of heat transfer efficiency. The less efficient the heat-transfer, the more the system has to work to provide the same level of service. And most so-called closed systems are not truly closed. There has to be provisions made to automatically compensate for any pressure changes or water losses in the system.