Heater not working on Ford Escort Mk5?

when I put heater on, no heat comes through even when the engine has reached it's working temperature. the hose to the thermostat housing is hot and the top one leading to the heater unit behind the bulkhead is also hot but the lower one is luke warm. I replaced the thermostat approx 1 year ago and have tested it out of the car with boiling water and it opens ok any ideas?

David Lee
November 2007