Im not wanting to take over anyone else'e heater problem thread so I made my own.

I have a 2002 F-150 5.4L with the electronic control module. MY heater is blowing cold air. When I hit the automatic button it blows cold air through the defrost, but when I hit the panel/floor button it blows cold air through the panel and floor. I originally thought it was the blend door or blend door actuator. But I checked the heater hoses going into the firewall and the one coming from the top of the engine gets hot and the other one stays cold. So I am now believing its either a clogged heater core or a bad heater core. I'm planning on trying to flush the core tomorrow and if that doesn't work just changing the core. As I was reading tonight some more, I saw something about the possibility of the thermostat being stuck open. If that was the case would one hose be hot and the other cold? Does anyone else have any advise on anything else I should check out? TIA.

 

Seems to me if the thermostat stuck open you would still eventually get heat after the whole system got hot.

 

I have been going thru the same thing with my sons 1997. I have flushed the heater core twice and the whole system once and it lasts for about a day. I am going to go ahead and replace the heater core soon.