Service Performed: System Inspection and Cycle Testing. Status: Resolved / Maintenance Recommendation Provided. Technical Observations Electrical Inspection: Inspected the furnace control board; identified and tightened loose thermostat terminal connections to ensure signal integrity. Operational Testing: Performed initial test fire with blower doors removed to verify sequence of operation. Reinstalled doors and confirmed successful ignition and sustained operation in both Stage 1 and Stage 2 heating cycles. Airflow & Limit Diagnostics: * Tested the system using the existing, heavily soiled air filter. Results: The furnace experienced a "High Limit" trip (overheating) after approximately 4.5 minutes. Subsequent testing mirrored the client’s reported symptoms, with the unit short-cycling (7 minutes ON / 3 minutes OFF). Root Cause: Restricted airflow due to the depleted filter caused internal temperatures to exceed safe operating limits, triggering a safety shutdown. Recom