7 FLASH
Armstrong Air
Flame Sense Failure
Furnace starts but shuts down; LED flashes 7 times repeatedly on Armstrong Air control board.
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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
Dirty or oxidized flame sensor, Poor burner ground, Low gas pressure causing weak flame, Faulty flame sensor or control board
How to Fix / Troubleshooting
Safety: Turn off power and gas before removing burner access panels. Components may be hot.
Steps to check:
- Clean flame sensor: Locate the flame sensor rod near the burner where the flame contacts it. Remove the mounting screw and gently clean the rod with fine steel wool or a Scotch-Brite pad until shiny. Do not use sandpaper that leaves deep scratches. Reinstall firmly.
- Check ground connections: Ensure the burner assembly and control board ground wires are tight and free of corrosion. A poor ground can prevent proper flame sensing.
- Inspect burner flame: With panels reinstalled and power restored, observe the burner flame through the sight glass. It should be steady and mostly blue. Yellow, lifting, or unstable flames may indicate low gas pressure or dirty burners.
- Test flame sensor signal (for technicians): Measure microamp current in series with the flame sensor lead during operation. Typical values are 1–5 µA DC. If the reading is low despite a good flame and clean sensor, suspect the control board.
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Repair Difficulty
Medium
3/5
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