No LED light, furnace completely dead

Safety: Use caution when working around live electrical panels.

Steps to check:

• Check breaker: Locate the furnace circuit breaker in the electrical panel. If tripped, reset once. If it trips again, do not continue resetting; call a professional.
• Verify service switch: Ensure the furnace service switch (often looks like a light switch near the unit) is ON.
• Door switch: Confirm the blower door is properly installed and depressing the door safety switch.
• Inspect board fuse: Remove the blower door and locate the low-voltage automotive-style fuse (3–5A) on the Trane control board. If blown, replace with the same rating. If it blows again, there is a short in the low-voltage circuit.

When to call a professional: If power is present but the transformer or control board is not outputting 24V, or if fuses keep blowing, contact a technician.