Taco 5000 mixing valve help

Recently installed a taco 5000-2 mixing valve in a radiant loop. My issue is the hot water is going in the Hot Inlet and Out the Cold inlet. It is also leaving the mixed outlet to the radiant loop but alot of the water is bypassing the loops and going directly to the return manifold. The thermostat for this radiant loop never gets satisfied because of it.
Is a check valve needed on the cold side to prevent this ? The valve is definately installed correctly with regards to hot/cold/mix.