Strange heating problems
 

Ok, my heat hasn't worked since the day I bought my car.
I finally got tired of my girlfriend shivering every time we go somewhere and decided to fix it. First I flushed, just the heater core. Then I decided to flush the rest. So I Filled it back up with water and a detergent I picked up for it, and let the engine run at operating temperature for 10 minutes. While I was doing this I was sitting in the car with the heat on full blast. it was coming out nice and hot. When I finished the flush and fired the car back up, it got warm. not hot. I knew it wouldn't be the greatest with a 160 degree thermostat. But it was alot better before. Any ideas?