Furnace will not start at all; no inducer, no blower, no LED lights on the Comfortmaker control board.

Safety: Before working on electrical components, turn off power at the breaker. Use a non-contact voltage tester if available.

Steps:

• Check breaker: Locate the furnace breaker in the electrical panel. If tripped, reset once. If it trips again, do not continue resetting.
• Check service switch: Ensure the switch near the furnace (often looks like a light switch) is in the ON position.
• Inspect blower door switch: Make sure the blower compartment door is properly installed and depressing the door safety switch.
• Check board fuse: Open the blower door and inspect the low-voltage fuse on the control board. Replace with the same rating if blown.
• Test transformer (if equipped): If you have a multimeter and are comfortable using it, check for 120V into the transformer and ~24V out. No output indicates a failed transformer.

When to call a technician: If power is present but the board is dead, or if the breaker continues to trip, professional electrical diagnosis is required.