The system works like this: The small panel at the far lower left of the console indicates the state of the system. There are two level-sensing probes in the collection tank. If the water drops below the lower probe the system opens a valve in the basement to add deionized water to the tank. This filling of the tank continues until the water reaches the upper probe (15-20 minutes) at which time the valve is closed. When the valve first opens, the "normal" light on the panel goes out and the red "low" light begins flashing. Simultaneously with this, a loud, annoying alarm begins screeching and the "trouble" light lights. The noise can be stopped by pressing the "audio off" button at the right side of the panel. Once the level has returned to "normal", the "trouble" light can be turned off by pressing on it. Nothing can be done at the control panel to stop the automatic fill. If power is removed from the system (e.g. during a power failure) and the level in the tank is anywhere below the upper probe, filling will commence until the water is again at the upper probe. Normally the level in the tank is checked during the weekly maintenance and if water is needed it is added with a manual fill valve, so if the system detects a low level and begins filling automatically this indicates an abnormal loss of cooling water.