Does a Taco mixing valve have a check valve in it to prevent the flow of hot water flowing back through the cold inlet side? The cold inlet feels as hot as the hot inlet. The mixed output feels about the same temp as the 2 inlets. I think the water is leaving the circulator on the hot input and flowing through the cold inlet instead of flowing through the mixed output through the floor loop. My thermostat is calling for heat and the circ is running but the room temp is down 3-4* and it never was before I added this mixing valve?