taco 5000 not working..??

we have a relatively new Taco mixer valve 5000...... cold going in ........ very hot coming out of the coil to the valve,,,,,,,, lukewarm ( at best) going into the domestic water system ! Cold showers !
I have the valved turned all the way ,counterclockwise (H) but still the same ,,,, Iturned it all the way back no change,
could the valve have failed , or could it be stuck, ( less then a year old.). city water ,,,,,, not hard,,,,

taco 5000: "Fail-Safe on Hot or Cold Supply Failure "


Have you checked with Taco and with the manufacturer of your tankless to see if that valve is appropriate for your application??