E9
American Standard
System Lockout / Multiple Faults Detected
Thermostat or control shows E9 and the system locks out after several failed start attempts
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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 high- or low-pressure trips, Persistent sensor faults, Control board internal error, Incorrect line voltage to American Standard equipment
How to Fix / Troubleshooting
Safety first: Turn off power to both indoor and outdoor units before inspection.
- Power cycle the system: Turn off breakers to the air handler and outdoor unit for at least 5 minutes to clear lockout. Restore power and observe operation.
- Check for underlying codes: Some American Standard controls will show a more specific code before E9. Note any additional codes or LED flash patterns on the control boards.
- Inspect line voltage: Verify that the outdoor unit disconnect is fully inserted and that there are no signs of burnt lugs or melted insulation. A technician should measure voltage to ensure it is within the nameplate range.
- Call for service if E9 returns: A recurring lockout indicates an unresolved underlying fault (pressure, sensor, or board). Continued resets without repair can damage the compressor or electronics.
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Repair Difficulty
Professional Required
5/5
Required Part
System Control Board
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