Furnace runs but some rooms remain cold or have very weak airflow.

Safety: Turn off power before opening duct access panels or working near moving parts.

• Check registers and dampers: Ensure supply registers in cold rooms are fully open. Locate and open any manual dampers in branch ducts serving those rooms.
• Inspect ducts: In accessible areas, look for crushed, kinked, or disconnected ducts and repair or replace as needed.
• Verify filter and blower: Replace dirty filters and confirm the blower is running at the correct speed tap for heating as specified by Miller.
• Balance system: Slightly close registers in overheated rooms to push more air to colder areas, but do not close too many as this can cause overheating.