Left picture is the bypass valve. Under that black box is the cold water shutoff valve which isn't visible. System is in bypass.
Center picture is the hot water shutoff valve currently in bypass.
Right picture is the bypass valve in bypass. Opening the cold and hot water valves with this valve not closed will give you cool to luke warm water vice hot water.
I access these valves under my sink, ACE 32.1, so yours may be elsewhere.