im having a problem with my car over heating on 2002 Subaru Impreza WRX

i think it my be my water pump i took the thermistat out and it was work but i decicded to put the thermistat back in befor winter and it wont put out heat out of the heater and it over heats

2 answers
Is the thermostat opening at the proper temp.? Does it overheat while driving at speeds over 35MPH? Was Proper coolant mix put in and air purged out of the system (warmed-up with heat on high -temp.-not fan speed)? Is radiator cooling fan cycling on when reaches operating temp.?
with the car running, check for random air bubbles in the coolant overflow tank, if theres any, chances are it's your head gasket.