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Error code reference

Lennox Furnace Error Code E126

Control internal communication problem.

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What the E126 error code actually means

Your Lennox furnace's main circuit board is having trouble communicating within itself, which has caused it to shut down and display this error. Think of it like the furnace's brain having a momentary glitch. In many cases, turning the furnace off and back on will clear the issue, but if the error keeps coming back, the control board itself will likely need to be replaced.

Diagnostic procedure

The full E126 procedure

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1
First diagnostic step
Cycle power on control. Replace if problem prevents service and is persistent.
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Most common causes of E126

Ranked by how often they cause this code
  1. 1Transient power event or voltage spike
  2. 2Failed or damaged control board
  3. 3Intermittent power supply to the control board
  4. 4Loose or corroded wiring connections at the control board

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Questions people ask about E126

What does E126 mean on a Lennox furnace?
E126 indicates a control internal communication problem, meaning the furnace's main control board has detected a fault within its own internal communication circuits. The board's processor is not operating or communicating correctly. This can result from a power disturbance or from an actual failure of the control board's internal components.
How do I fix E126 on my Lennox furnace?
Start by turning the furnace off at the disconnect switch or breaker, waiting 30 seconds, and restoring power. If the furnace resumes normal operation, no further action is needed. If E126 returns persistently, the control board will need to be replaced by a qualified technician, as the internal fault cannot be repaired in the field.
How much does it cost to fix an E126 error on a Lennox furnace?
If a power cycle resolves the issue, there is no parts cost. If the control board requires replacement, parts and labor typically range from $300 to $700 depending on the specific board model and local labor rates. A diagnostic service call to confirm the fault and rule out other causes will usually add $75 to $150 to the total cost.
Will resetting the furnace clear the E126 error?
Cycling power to the furnace is the first recommended step and will clear E126 if the fault was caused by a transient event such as a power surge or momentary brownout. If the code returns after the power cycle, the problem is persistent and points to a hardware failure on the control board that resetting alone will not fix.
Is it safe to run my Lennox furnace with an E126 error?
When E126 is active, the furnace is typically prevented from completing normal operation, so it will not be heating your home. The error itself is a board-level communication fault and does not indicate a gas leak or combustion hazard. However, you should not attempt to bypass the fault, and the furnace should be repaired before relying on it for heating.

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