A heater assembly for an injection molding apparatus comprises a heater sleeve having a threaded inner surface for engaging a threaded outer surface of a nozzle body of a nozzle or a threaded surface of a mold manifold. A clamping element such as a lock nut or a spring is provided adjacent the heater sleeve. The lock nut and/or the spring abuts the heater sleeve to force the threaded inner surface of the heater sleeve into contact with the threaded outer surface of the nozzle body. This removable clamped heater assembly operates regardless of the temperature of heater.