Furnace will not run; status LED shows 7 flashes repeating; blower may run on low speed.
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 removing burner access panels. Allow the furnace to cool.
Corrective actions:
- Clean flame sensor: Remove the flame sensor and clean the rod with fine steel wool or emery cloth until shiny. Reinstall and ensure the mounting screw is tight.
- Check burner flame: With panels reinstalled and power restored, observe the burner flame through the sight glass. The flame should be steady, mostly blue, and should fully engulf the flame sensor. Yellow tipping or lifting flames may indicate combustion or gas pressure issues.
- Verify ground connections: Confirm that the burner rack and furnace cabinet are properly grounded. Tighten ground screws and clean rusted surfaces.
- Inspect gas supply: Ensure the gas shutoff valve is fully open. If other gas appliances show issues, contact the gas utility. Low inlet pressure can cause flame dropout.
- Check wiring to gas valve: Inspect the harness from the control board to the gas valve for loose or damaged wires.
Professional help: If flame remains unstable or the fault persists after cleaning and checking grounds, a technician should check gas pressures and possibly replace the gas valve or control board.