Furnace will not start; status LED shows 5 red flashes repeating; blower may run continuously.
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety first: Turn off power and gas to the furnace before inspecting flame components. If you smell gas when the furnace is off, contact your gas utility immediately.
Steps to check:
- Inspect flame sensor and wiring: Locate the flame sensor rod near the burners. Remove the mounting screw and inspect the ceramic insulator for cracks and the rod for heavy oxidation. Check the wire from the sensor to the control board for damaged insulation or contact with metal.
- Clean flame sensor: Gently clean the metal rod with fine steel wool or emery cloth until shiny. Do not sand the ceramic. Reinstall and ensure the rod is properly positioned in the burner flame path.
- Check for stray voltage or shorts: With power off, verify the flame sensor wire is not pinched under panels or touching sharp metal edges. Reroute or secure as needed.
- Control board evaluation: If the error persists after cleaning and inspecting the sensor and wiring, the integrated furnace control (IFC) board may be misreading flame current. Board diagnosis and replacement should be performed by a qualified technician.
Do not attempt to adjust or disassemble the gas valve. Any suspicion of gas leakage or valve malfunction requires professional service.