Since its starting to get colder outside I decided it was time to figure out why me heater isn't working... I did just put a new water pump and thermostat in. I checked the heater control valve and its working (hot water on both sides of the valve) but the hose coming out of the heater core it stays cold. So I guess that my heater core is plugged... What is the best way to flush it out?? Or am I just wasting my time and it just needs to be replaced... I read up on here, but all I found was that the outside was plugged with leaves and stuff... nothing about the inside. I'm going to try a coolant flush but other ideas more than welcome... Thank you in advance..

 

So I pulled the hoses off going to the heater core and flushed it out with a hose (a ton of garbage came out) and put everything back together. Now the heater works like it supposed to, but now the truck is running hot. Gotta flush the whole system now. We'll see how it goes.

 

I think you're on the right track, there's a pretty good chance you moved some gunk downstream in the system. Maybe somebody used some stop leak or something, that always ends up in the heater cores.

 

So I flushed the system, drained it, then added some Radiator & Coolant System Cleaner. They say to run it for around 10 hours of normal driving and then flush again and fill with coolant. I've never run the stuff so we'll see how it works.
Fingers are crossed!!!!

 

i did exactly this and it was all that was required. the hose popped off a couple times and got me real good