mypros+
Error code reference

Lennox Air Conditioner Error Code E125

There is a hardware problem with the outdoor control.

Lennox codesLennox air conditioner codes
Avg. service call
$285
National average. Trip fee plus diagnostic plus labor. Before parts.
MyPros+ 3-day pass
$9.95
Same diagnostic steps, on your phone. Start now.
You keep in your pocket
~$275
Even before you buy the part.
Skip the service call. Fix it yourself.
Full procedure unlocks instantly.
Get Started

What the E125 error code actually means

Your Lennox air conditioner is reporting a problem with the main computer board located in the outdoor unit. This board controls the most important functions of your system, and the unit may not operate correctly or at all until the issue is resolved. A technician will need to inspect and most likely replace that control board to get your system running again.

Diagnostic procedure

The full E125 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.

MyPros+ · DiagnosticsStep 1 preview
1
First diagnostic step
Replace the outdoor control if the problem prevents operation and is persistent.
Unlock with pass
Unlock with pass
Unlock with pass
More steps, wiring diagram references, and verified part numbers
Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.
Unlock E125 procedure $9.95

Or subscribe: $29/month for unlimited access to all codes plus Max AI diagnostics.

Most common causes of E125

Ranked by how often they cause this code
  1. 1Failed outdoor control board
  2. 2Power surge or lightning damage
  3. 3Moisture or corrosion on the board
  4. 4Overheating of the control board
  5. 5Loose or damaged wiring to the outdoor control

Most DIYers save hundreds by diagnosing before ordering parts.

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass

Questions people ask about E125

What does E125 mean on a Lennox air_conditioner?
E125 indicates a hardware problem with the outdoor control board in your Lennox air conditioner. The outdoor control board manages compressor and fan operation as well as system communication. This code means the board itself has experienced an internal fault rather than a problem with a sensor or refrigerant level. Persistent occurrences require inspection and likely replacement of the outdoor control board.
Is it safe to run my Lennox air conditioner with an E125 error?
If the E125 error is persistent and preventing normal operation, the system should not be forced to run. A failed outdoor control board can cause unpredictable behavior including compressor or fan motor issues. Continued operation with a compromised control board may risk additional component damage. Power the system off and contact a technician promptly.
How much does it cost to repair a Lennox E125 error?
Repair costs for E125 depend primarily on the cost of the replacement outdoor control board and the labor involved. Parts costs for outdoor control boards typically range from around $150 to $500 or more depending on the specific Lennox model, and labor charges can add another $100 to $300 depending on your region and service provider. Getting a diagnostic estimate from a certified Lennox technician before authorizing the repair is advisable.
Can I fix E125 on my Lennox air conditioner myself?
Diagnosing and replacing the outdoor control board requires familiarity with electrical components and safe handling of line-voltage circuits, so this repair is best left to a licensed HVAC technician. A technician will verify the board is the root cause by inspecting it for visible damage, checking input voltage, and ruling out wiring faults. If the board is confirmed faulty, replacement is the required fix.
Will resetting my Lennox air conditioner clear the E125 error?
A power reset may temporarily clear the error display, but if the underlying hardware fault in the outdoor control board remains, the E125 code will return. Because this code reflects an internal board hardware condition rather than a transient sensor reading, a reset alone is not a reliable fix. Replacement of the outdoor control board is the recommended resolution for persistent occurrences.

Related Lennox air conditioner error codes

All Lennox air conditioner codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass