Just recently I replaced the blower motor relay.

Just recently I replaced the blower motor relay and my A/C now works just fine. My Thermostat Control appears to be working just fine. However whenever I press the Econ. Button to produce heat and it does blow but just not Hot. Not even If It has been running for 10 minutes. All the while my Thermostat Control reads 85*. Now I have had the glove box out and inspected everything visual and all looks well. I can clearly see the flap door motor engaging or so it appears. I can see a rod sliding. Now if the fan is running, the stat is adjusted properly, and I'm not loosing any coolant through the heater core it should produce heat. However if the flap door is not properly opening and closing would not allow heat to mix with the air. So knowing all of the facts can you tell me what else would prevent my heater from working?