Lennox Furnace Error Code E 273

E 273 is a soft lockout code indicating the furnace exceeded the maximum number of allowed ignition recycles, with the last failure caused by the control board not detecting a flame. The furnace stops attempting to light as a safety measure. The most common cause is a dirty or failed flame sensor that cannot pass adequate micro-amperes through the flame to signal the control board. The code will clear on its own once a heating cycle completes successfully after the underlying issue is resolved.

E 273 is a soft lockout, which means it does not require a manual reset to clear. The code will clear automatically once a heat call completes successfully from start to finish. However, simply resetting the furnace without addressing the root cause will likely result in the code returning after another series of failed ignition attempts.

If the fix is simply cleaning the flame sensor, costs are minimal and may only involve a service call fee, typically in the range of $75 to $150. If the flame sensor needs to be replaced, parts and labor together generally range from $100 to $250 depending on the technician and region. If the control board is at fault, repair costs can rise significantly, often falling in the $300 to $600 range or higher depending on the specific board and labor involved.

Start by using the furnace control board's built-in diagnostics to read the actual microamp output of the flame sensor. If the reading is low, carefully clean the sensor rod with fine steel wool or emery cloth to remove oxidation. Next, measure the voltage between neutral and ground at the unit to confirm a solid electrical ground. If cleaning does not resolve the issue, replacing the flame sensor is the next step.

The lockout itself is a safety feature designed to prevent the furnace from repeatedly attempting to ignite without confirming a flame is present. While the furnace is in lockout it will not heat your home, but it is not producing an immediate hazard. You should still address the fault promptly, particularly if there is any concern about gas supply or ignition components, and ensure any repairs are performed by a qualified technician.