Thermostat calls for heat but furnace does nothing; no inducer, no blower, LED shows normal idle.

Safety: Turn off power before working on low-voltage wiring.

Steps to check:

• Check thermostat: Replace batteries if applicable and ensure settings are correct.
• Inspect wiring at furnace: Confirm the W wire is securely attached to the W terminal on the control board and not broken.
• Test with jumper: With power off, temporarily connect a jumper between R and W at the control board. Restore power. If the furnace starts, the thermostat or its wiring is likely faulty.

When to call a technician: If the furnace does not respond even with R-W jumpered, professional diagnosis of the control board and safeties is needed.