Furnace will not start; status LED shows 1 flash repeating, inducer and blower are off.

Safety first: Turn off electrical power to the furnace at the service switch and shut off the gas at the gas cock before removing panels. If you smell gas continuously, evacuate and contact the gas utility or a licensed technician immediately.

Step-by-step checks:

• Verify thermostat call for heat: Set thermostat to HEAT and raise the setpoint 5–10°F above room temperature. Confirm 24 VAC between R and W at the furnace control board.
• Check gas supply: Ensure the manual gas shutoff valve to the Concord furnace is fully open. If other gas appliances are also not working, the issue may be with the gas supply to the home.
• Inspect hot surface ignitor (HSI): Remove the burner access panel. Locate the silicon carbide or silicon nitride ignitor near the burners. Look for cracks, white spots, or breaks. If damaged, replace the ignitor with the correct Concord-compatible part and avoid touching the element with bare fingers.
• Clean or inspect flame sensor: Locate the flame sensor rod at the burner assembly. Remove the mounting screw, gently clean the rod with fine steel wool or emery cloth, wipe with a clean dry cloth, and reinstall. Ensure the sensor wire is firmly connected to the control board FLAME or FS terminal.
• Check wiring to gas valve and ignitor: Inspect harnesses from the integrated furnace control (IFC) to the gas valve and ignitor for loose plugs, burned connectors, or damaged insulation. Reseat any loose connectors.
• Restore power and test: Turn gas and power back on, then call for heat. Observe the ignition sequence through the sight glass. If the ignitor glows but burners never light, suspect the gas valve or gas pressure. If the ignitor never glows, suspect the ignitor or IFC.

When to call a professional: If you are not trained to work with gas valves or cannot verify gas pressure with a manometer, contact a qualified HVAC technician. Do not attempt to adjust gas pressure yourself.