Lennox EL296UHV Error Code E 125: Control Self-Check Failure

What Does Code E 125 Mean?

Error code E125 on the Lennox EL296UHV indicates that the control board has detected an internal hardware failure during its self-diagnostic check. This is a critical alert covering hardware errors such as flame sense circuit faults, pin shorts, and other internal component failures.

The control board runs periodic self-checks to verify that its internal circuits are functioning correctly. When a hardware error is detected, the board may not be able to safely manage ignition sequences, flame monitoring, or other safety-critical functions. The system will attempt to restart if the error condition clears on its own.

Cycling power to the furnace (turning off the circuit breaker for 30 seconds, then turning it back on) can sometimes clear a transient E125 caused by a voltage spike or temporary electrical disturbance. However, if the error returns after power cycling, the control board has a persistent hardware fault and needs to be replaced. The fault clears 300 seconds (5 minutes) after the hardware error recovers, if it recovers at all.

Common Causes

When to Call a Professional

Contact a licensed HVAC technician if:

• E125 returns after power cycling the furnace
• The furnace cannot heat and shows E125 as a critical alert
• Other error codes appear alongside E125

✓ Verified against manufacturer service manual — March 2026