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

Safety: Use caution around electrical panels. Turn off main power if necessary.

Steps:

• Check breaker: Locate the furnace breaker in the electrical panel and reset it if tripped. If it trips again immediately, call a professional.
• Verify furnace switch: Ensure the furnace service switch (often looks like a light switch) is ON.
• Door switch: Confirm the blower door is properly installed and depressing the door safety switch. Some models will not power up with the door removed or misaligned.
• Inspect internal fuse: With power off, check the low-voltage fuse on the control board and replace it if blown.

If there is still no power or LED, the transformer or control board may have failed and should be tested by a technician.