The building was new. The system was new. The problem persisted anyway, through multiple contractor visits, each of which found nothing conclusive and each of which left the fault exactly where it was.
That pattern is the tell. When several competent people attend the same fault and none of them fixes it, the fault is usually not where they are all looking.
The work was to review the installation as a whole rather than the last thing that failed, to challenge the assumptions the previous attendances had shared, and to coordinate the right expertise onto the question.
What changed my thinking
Reviewing the installation as a whole identified system-level configuration issues that individual component checks had missed. Once the system was properly understood, the fault was resolved. The experience reinforced the importance of giving one person responsibility for the complete technical question.
Botan Hourami