Two years ago my heat decided to stop working, nothing but cold air. Took it to the dealer...They said it needed a new heater core, $800.00.

Took it to another dealer, they looked at it, flushed it. It had slight heat...it was nearing the end of Winter so I figured I'd fix it in the Fall (Heater Core).

The next year came....Once again, I had heat, just like normal could cook eggs on the dash, never a problem all year.

Now, this Winter....Nothing, No heat, just blows cold air.

I have a hard time believing it is the heater core....Any suggestions (Changed the themostat)...possibilities...Anyone have the same problem???

2000 Blazer by the way (TrailBlazer Package), 68000 miles.

when you move the lever to defrost do you hear a movement under the dash and do you get heat here? same goes for when you switch to say .. floor heat you should hear the sound of the flapper moving - if not could be a problem with the vacum motor .

Is the heater core return hose warm? If not there is no flow thru the core... then you should back-flush it (again) and se if it works.

I had a leak in my core and it was not funny to change it, took say 6 hours...
/Freddy

Blending door motor.

Do a search, the gear will often strip and the air will no longer be pushed through the heat core for heat.

Search for blending door.