Furnace locks out; burners do not light; status LED shows 5 flashes repeating.
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: Turn off power and gas before servicing. This fault indicates a control or sensing issue that can be hazardous if misdiagnosed.
Troubleshooting steps:
- Inspect flame sensor and wiring: Locate the flame sensor rod at the burner. Ensure it is not touching the burner or grounded metal except at its mounting bracket. Check the sensor wire for damaged insulation or pinched sections against the cabinet. Repair or replace as needed.
- Clean flame sensor: Remove the sensor and gently clean the rod with fine steel wool. Reinstall and ensure a snug connection at the control board FLAME terminal.
- Check burner ground: Verify that the burner assembly and furnace chassis have a solid ground connection back to the electrical service. Tighten ground screws and clean any rusted contact points.
- Inspect control board: Look for signs of moisture, corrosion, or burned components on the integrated furnace control. If the board is reading flame when no flame is present and wiring is good, the board may be defective and require replacement.
Recommendation: Because this involves flame rectification circuitry, replacement of the control board should be performed by a qualified technician familiar with Concord furnace controls.