There isn't much to a heater cartridge, but they can fail. It's also possible that the wiring connections for the heater are failing. Consider to check the points in the wiring where it changes in any manner. If you have a direct wire from the heater cartridge to the main board, examine the connectors at the main board. If the connection is weak, it will heat up in the connection block instead of the heater. If it deteriorates sufficiently, you could have fire.

Useful information to provide for your future posts would be the model printer you are using.