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Error code reference
Lennox Furnace Error Code LED1-FAST_FLASH/LED2-FAST_FLASH
Normal operation
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What the LED1-FAST_FLASH/LED2-FAST_FLASH error code actually means
This LED pattern simply means your furnace has received the signal from your thermostat to start heating and is beginning its startup process. It is not a problem or error. Your furnace should continue through its normal startup steps and begin heating your home within a minute or two.
Diagnostic procedure
The full LED1-FAST_FLASH/LED2-FAST_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.
More steps, wiring diagram references, and verified part numbers
Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.
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Most common causes of LED1-FAST_FLASH/LED2-FAST_FLASH
Ranked by how often they cause this code
- 1Normal thermostat heating demand
- 2Thermostat set point raised above room temperature
- 3Furnace returning from a standby or off state
- 4Thermostat wiring completing the W-terminal circuit
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Questions people ask about LED1-FAST_FLASH/LED2-FAST_FLASH
What does LED1-FAST_FLASH/LED2-FAST_FLASH mean on a Lennox furnace?
This LED pattern indicates normal operation and signals that a heating demand has been initiated at the thermostat. The control board has received the call for heat and is beginning the ignition startup sequence. No fault condition is present when this pattern appears.
Is it safe to run my Lennox furnace when it shows this LED pattern?
Yes, this pattern is a normal operational status and does not indicate any safety concern. The furnace is functioning as designed when displaying this code. If you have concerns about furnace operation beyond this status, such as unusual smells, sounds, or failure to heat, those should be investigated separately.
Will resetting my Lennox furnace clear this LED pattern?
Resetting the furnace will temporarily clear the LED display, but the pattern will return as soon as the thermostat initiates the next heating demand. Since this is a normal status indication rather than a fault, clearing it through a reset is neither necessary nor beneficial to furnace operation.
Do I need to fix anything when I see this LED pattern on my Lennox furnace?
No repair or intervention is needed for this LED pattern by itself. It is a normal status indication that the furnace has received a heat call. If the furnace fails to complete its startup cycle and begin heating after this point, then a separate diagnostic step would be needed to identify the downstream cause.
How much will it cost to resolve the LED1-FAST_FLASH/LED2-FAST_FLASH code on my Lennox furnace?
Because this LED pattern represents normal operation rather than a fault, there is no repair cost associated with it. If a technician visit is needed to confirm the furnace is operating correctly, a standard diagnostic service call typically ranges from $75 to $150 depending on your location and provider.
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