06 E350 4Matic has no heat. Why.

What is your question?

vehicle temprature reaches normal hi about 80. I installed new thermostat. AC works. Blower works. But NO hot air.

What makes this problem better or worse?

always same

How long has your 2006 Mercedes-Benz E350 had this problem?

heat was not very good last winter. I installed new thermostat but was the same. Now when it got cold and I turned on heat, there is NO HEAT out of vent although engine temp is OK.