What would cause my heater to stop blowing hot air? on 2003 Ford F-150

Recently my heater quit blowing hot air. I have replaced the thermostat, after the problem occurred. This was done at the recommendation of a Ford certified mechanic at our local Ford Dealership. He felt my top hose, which was hot, then bottom hose. The bottom hose was only warm. He thought it might be sticking some. I have inspected all hoses, fuses, relays and vacuum lines. All appear to be in good operable working order. I have never had any wetness or dampness on the floorboard of the truck indicating a heater core issue. Some have mentioned possible heater control valve but I have not been able to locate this item either in the engine compartment or in the dash against fire wall. I'm at a loss on where to go next. Any advice no matter how stupid or inconsequential you may think it may be would be greatly appreciated. Thanks. Very Frozen Turtle

by in Ellisville, MS on December 16, 2013
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1 answer 1 comment
ANSWER by , December 16, 2013
I would try and flush the heater core out to start with
COMMENT by , December 17, 2013
Do you mean directly? Does this past not flush when doing a system flush of the radiator? I really don't know is why I'm asking.