Furnace runs but some rooms are cold while others are warm.

Safety: Turn off power before opening panels; duct inspection in accessible areas is generally safe.

• 1. Check registers and dampers: Ensure all supply registers are open and any manual dampers in ducts are properly positioned.
• 2. Inspect accessible ducts: Look for disconnected or crushed flex ducts in basements or attics.
• 3. Replace filter: Install a clean filter to restore full airflow.

Persistent imbalance may require duct modifications by an HVAC contractor.