The furnace will not start at all; there are no lights, no blower, and no inducer operation.

Safety first: Use caution when working around electrical panels.

• Check breaker: Locate the furnace breaker in the electrical panel and ensure it is ON. If tripped, reset it once. If it trips again, call a professional.
• Service switch: Verify that the furnace service switch (often looks like a light switch near the unit) is ON.
• Door switch: Ensure the blower compartment door is properly installed and depressing the door switch.
• Control board fuse: With power OFF, inspect and replace the low-voltage fuse on the control board if it is blown.

If the furnace still shows no signs of life, the transformer or control board may have failed and should be tested by a technician.