2001 f 150 heater warms up but not hot at all
Make sure that the engine is at normal operational temp, a stuck open thermostat can cause low heater output, if that checks good then you need to see that all the blend doors are operating correctly and your not mixing cold air with heated air, and if those check good then the heater core is most likely partially plugged. HTH
Also check the line from the radiator to the heater core. There is usually a valve attached with operates on vacuum to keep it open. As a safety precaution the valve is always open supplying hot water to the core in the event someone gets stranded in frigid locations. If the engine runs, the heater will work, absent a blend door, actuator problem.
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