No heat/bottom radiator hose cold

I would say either the thermostat is a poor quality replacement part. Or the vehicle has a flow problem such as worn water pump impelars or a resticted radiator. The last thing could be a large air pocket which is possible if the proper fill and bleed procedure wasnt followed with the thermostat replacement

Hold the garden hose tightly to the outlet of the core "bottom hose" have someone turn the hose on hi till clean water freely runs out the other tube, reassemble worked great for me after thermostat did not help