No heat Heater core is hot - 2001 Dodge Ram 2500 Truck

SOURCE: no heat inside van

THERE IS A DOOR UNDER THE DASH THAT MOVES FROM COOL OR AC AIR TO HEAT CHECK AND MAKE SURE ITS MOVING WHEN CHANGING SETTINGS

SOURCE: heater not heating hot enough. heater core not

Good place to start is a cooling system flush and thermostat replaced.

SOURCE: how do I replace a heater core on a 1998 jeep wrangler

An addtion to the above Check to be sure the radiator level is full first.

SOURCE: no hot air from heater, blower runs fine

The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow. If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm. If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air. If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted. One or a combination of these factors is likely the culprit in your case.

Since you state the 2 things you ruled out, that leaves only the water pump. Is the car running hot? The thermostat may be sticking as well... but im leaning toward the pump.

SOURCE: Prizm overheats, heater core leaks, no heat

You can bypass the core or fix it that's up to you but I would change or remove the thermostat first. If it still overheats then start looking at the water pump and radiator. Hope this helps. Good luck.