Hello Steven,
A loose / not fully seated tip is the most likely source of the problem.
Actuator Fault is meant to be a general warning message. In the case of the soldering iron, this means there is an error with the heating element. The heating element on the iron is in the tip.
The iron is trying to heat up but the temperature sensor is unable to read that the tip is heating up. This will cause the actuator fault. The fault is a safety feature to prevent run away heating.
You can try power cycling the iron by removing the power cord and reseating the tip. If the error continues please reach out to our Customer Support team (support@ifixit.com) and they will be able to help.