Lennox EL296UHV Error Code E 273: Soft Lockout - Flame Failure

What Does Code E 273 Mean?

Error code E 273 on the Lennox EL296UHV is a flame-failure soft lockout. The furnace lit and proved flame, but the flame signal dropped out during the run. Each time that happens the control closes the gas valve for safety and recycles, and after exceeding the maximum number of recycles the SureLight integrated control declares a soft lockout. As with the model's other soft lockouts, it recovers on its own once a heat call finishes successfully rather than needing a manual reset.

The difference from E 270 is a matter of when the flame is lost. E 270 (ignition-failure soft lockout) means the control never sensed flame current across any of its ignition retries. E 273 means the flame did light and prove, then failed part way through — the furnace was heating and lost the signal. That points to a flame that is present but marginally detected, which is why the leading cause is a flame sensor that has accumulated a film and no longer reads a steady current. You may also see E 240 (low flame current) logged before or alongside E 273 as the signal weakens.

A poor unit ground is the other common cause on this control, because flame sensing relies on a good ground path to read microamps reliably; when the ground is marginal the control can lose the flame signal even though combustion is fine. Intermittent gas pressure can produce the same drop-outs less often. Cleaning or replacing the flame sensor and verifying the ground are technician tasks on this model — they involve accessing the burner area and measuring flame current, so they are not homeowner steps.

What You'll Notice

• The furnace lights and heats for a short time, then shuts off
• This light-then-drop-out pattern repeats several times before the furnace stops
• The seven-segment LED shows E 273 (and sometimes E 240 in the history)
• The home warms slightly during each short run but never reaches the setpoint
• You may hear the gas valve click closed mid-cycle as the flame is lost

Common Causes

How This Is Diagnosed

A technician measures the flame sensor's current in microamps using the control's diagnostics while the burners are lit, watching whether the reading is low or drifting toward the drop-out threshold. Because a fouled sensor is the most common cause, they inspect and clean or replace the sensor rod as needed — a professional task that involves working in the burner area.

If the flame current is healthy, they check the unit ground by measuring neutral-to-ground voltage, since a poor ground is the next most likely reason the control loses an otherwise good flame. Only after those check out would they look at gas pressure stability as a less common cause.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• The furnace repeatedly lights and then drops out within a few minutes
• E 273 and E 240 (low flame current) both appear in the history
• The code returns after the burner area was recently serviced
• The flame looks weak, yellow, or unsteady when the burners are lit
• You suspect a grounding or gas-supply problem

✓ Verified against manufacturer service manual — March 2026