1. Triage safety
Identify combustion, electrical, refrigerant, condensate, and indoor-air hazards before routine diagnosis.
2. Measure
Review temperatures, pressures, airflow or water flow, controls, distribution, envelope, venting, drainage, and operating sequence.
3. Define the scope
Replacement scopes should identify load assumptions, equipment, distribution changes, electrical, permits, controls, and commissioning.
4. Start up and verify
Performance checks, control setup, airflow or hydronic balance, drainage, documentation, and owner orientation complete the work.