8 FLASHES
Ruud
Low Flame Sense or Ignition Lockout (alternate Ruud boards: Line Voltage Fault)
Status LED shows 8 flashes, furnace will not run, blower may run continuously.
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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.
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Possible Causes
Repeated failed ignition attempts, Flame sensor not detecting flame, Hot surface ignitor weak, Control board lockout after multiple retries
How to Fix / Troubleshooting
Safety: Turn off power and gas before servicing. Do not repeatedly reset a furnace that fails to ignite; determine the cause.
Steps to check:
- Power reset: Turn off furnace power for 5 minutes to clear lockout, then restore power and observe the ignition sequence.
- Check ignitor glow: During a call for heat, verify the hot surface ignitor glows bright orange. A dim or non-glowing ignitor should be replaced.
- Clean flame sensor: As described in the 7 FLASHES procedure, clean and reposition the flame sensor.
- Inspect gas valve operation: Listen for the gas valve click after the ignitor heats. If there is no click and no gas odor, the valve may not be opening. This requires professional diagnosis of the gas valve and control board.
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Repair Difficulty
Hard
4/5
Required Part
Hot Surface Ignitor
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