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Error code reference
Lennox Furnace Error Code LED1-SLOW_FLASH/LED2-SLOW_FLASH
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What the LED1-SLOW_FLASH/LED2-SLOW_FLASH error code actually means
Both LEDs slow-flashing on your Lennox furnace is actually a good sign. It means your furnace is powered up and working normally, or it is running the fan for cooling or air circulation. There is nothing wrong with your system when you see this light pattern.
Diagnostic procedure
The full LED1-SLOW_FLASH/LED2-SLOW_FLASH procedure
Step 1 is visible so you can confirm you are on the right page. The remaining steps, the ones that tell you whether to actually replace a part, unlock with any pass.
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1
Confirm the fault
Power cycle the unit: switch off the breaker for 60 seconds, then restore power. If the code returns, the fault is persistent and the procedure below isolates the cause.
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Most common causes of LED1-SLOW_FLASH/LED2-SLOW_FLASH
Ranked by how often they cause this code
- 1Normal powered standby
- 2Active cooling cycle
- 3Continuous fan mode active
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Questions people ask about LED1-SLOW_FLASH/LED2-SLOW_FLASH
What does LED1-SLOW_FLASH/LED2-SLOW_FLASH mean on a Lennox furnace?
This LED pattern indicates normal operation. It appears when the furnace is powered on and in standby, when the system is in an active cooling cycle, and when the thermostat is calling for continuous fan operation. It is a status indicator, not a fault or error code, and no corrective action is needed.
Is it safe to run my Lennox furnace when both LEDs are slow-flashing?
Yes, this pattern is a safe-operation indicator. All safety circuits monitored by the control board are satisfied when this pattern is displayed. There is no hazard associated with this LED status.
How much does it cost to repair a Lennox furnace showing this LED pattern?
No repair cost applies to this LED pattern because it indicates normal operation rather than a fault condition. If you are experiencing a performance issue alongside this pattern and a technician visit is needed to diagnose a separate underlying problem, service call fees typically range from $75 to $150 depending on your region and provider.
Do I need to fix anything when I see both LEDs slow-flashing on my Lennox furnace?
No repair or intervention is needed. Both LEDs slow-flashing is a confirmation that the control board is powered and operating normally. If you are seeing this pattern but your system is not heating or cooling as expected, the issue lies elsewhere, such as at the thermostat settings or a separate component, and the LED pattern itself is not pointing to a fault.
Will resetting the furnace clear the LED1-SLOW_FLASH/LED2-SLOW_FLASH pattern?
A reset will momentarily interrupt the pattern during the power-down cycle, but the slow-flash pattern will return as soon as the control board reinitializes, because it reflects normal operating status. Since this is not a fault code, there is nothing to clear.
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