engine is running and hot. have the blower inside the car on a fairly high speed. one hose should be slightly cooler than the other; the colder the air outside is the cooler the return hose will be. the heater has taken heat out of the water.
if not comfortable with working around a running engine you can do the touch test immediately after shutting off the engine.
if one hose is a lot cooler, you may have a blocked heater core.
3) your temperature blend motor on the heater case inside the car is not working. motor dead or door is stuck.
if you are comfortable under the dash, you can remove the 