Furnace cycles on and off frequently (short cycles) and the house temperature fluctuates.

Safety: Turn off power before accessing internal components.

Steps:

• Check thermostat location: Ensure the thermostat is not near supply registers, exterior doors, or heat sources. Relocation may be needed.
• Clean flame sensor: Remove and clean the flame sensor to prevent nuisance flame loss.
• Check filter and airflow: Replace dirty filters and open registers to reduce high limit trips.

Note: If the furnace is significantly oversized for the home, only a system redesign can fully correct short cycling.