The GC/MS 7890/5977 was found to have terminated a run due to a HIVAC not ready error. However, the instrument appeared fine and the run was restarted without any further issues for that run. However, this same error has happened a couple more times with the instrument being able to be restarted again without issue. What could be triggering the issue but also leaving he instrument is working order when found. We have already replaced the Pfeiffer pump hoping that would fix it but it did not.