The furnace starts then shuts down after a few minutes; the house never warms up.

Safety first: Turn off power before servicing.

• Step 1 – Replace filter: Install a new filter of the correct size and type.
• Step 2 – Check vents: Open all supply and return vents and remove obstructions.
• Step 3 – Blower operation: Verify that the indoor blower starts promptly and runs smoothly. If not, the motor or capacitor may be faulty and should be replaced.
• Step 4 – Clean heat exchanger: Have a technician clean the heat exchanger and check the limit switch.