I know there has been a lot of discussion on this topic, but can't find answer with search.

2003 530i just blows cold air even with heat set to 90 degrees. Temp guage at 12 o'clock. Does not overheat. Automatic Temp Controls, so has three hoses on firewall. Hoses cold on both sides of heater valve. System has been bled just too be sure. This car has the black expansion tank with 2 hoses. 1 of the hoses runs to what I beleve is the secondary water pump. With car at operating temp, this hose is cold, however, the hose on the other side of this unit which is at the bottom left of the radiator is hot. Is this the 2nd pump? I can hear water moving with iginition on and heater at 90 degrees with fan at lowest setting, and coolant comes out of the bleed screws as well. What is this thing, and if it's the 2nd pump, could it still be bad and not allowing the heater core to get hot?