One day plenty of heat, next day no heat. Expansion tank a little low, but plenty of water in the radiator. Topped of expansion tank, but no heat at all. This is an '08 with 50k. I can't believe that the heater core is plugged. Is there a valve to allow hot water in the heater core that may be inop? Any ideas before I run it to the dealer?
Yes, there is a control that controls the heat coming into the passenger compartment. I am assuming that the engine temp gauge shows normal temp and the DIC shows a temp around 190 degrees which mean the engine cooling system is fine. An actuator motor opens and closes a vent door that allows air to flow over the heater core sending heat into the passenger compartment.
WHAT I WOULD CHECK FIRST are the fuses in the floor console, look in your owner manual if you are not acquainted with where that is. Check fuse # 10 and 16 which may deal with heat/Ac. There is a panel you have to remove to get to the actuator sw and if you aren't into messing with mech stuff, and don't know what you really are looking, then go see a mechanic and help the economy. Always check fuses first.
This problem turned out to be a broken acuator arm.
This arm is integral to the heater box and everything had to be replaced. This also meant taking out the entire dashboard, two days labor and about $1,000. This is ridiculous on a two year car!