Furnace will not run; LED shows 5 flashes; 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: Turn off power and gas before inspecting flame sensor or gas valve. If you suspect a gas leak, do not attempt repair yourself.
Steps:
- Inspect flame sensor: Remove the flame sensor rod and check for cracks, corrosion, or contact with metal surfaces. Clean lightly with fine steel wool and reinstall, ensuring it is properly positioned in the burner flame path.
- Check wiring: Inspect the flame sensor wire from the sensor to the control board for damage or chafing to ground. Repair or replace damaged wiring.
- Verify proper grounding: Ensure the furnace cabinet is properly grounded and that neutral and ground connections are tight at the control board and junction box. Poor grounding can cause false flame signals.
- Observe gas valve: With gas on and power off, do not attempt to disassemble the valve. If you smell gas or suspect the valve is leaking, shut off gas and call a licensed technician immediately.
If cleaning the flame sensor and correcting wiring/grounding does not clear the 5-flash code, the control board or gas valve may be defective and should be diagnosed and replaced by a professional.