Lennox furnace E270: Soft lockout — retries exceeded, no flame current sensed
E270 means the furnace used up its ignition retries and never sensed any flame current at all. It is the lockout for a furnace that is not lighting, as opposed to one that lights and loses the flame.
Applies to: Lennox gas furnaces with a seven-segment diagnostic display on the control board, such as the ML193UHEK, per installation instructions 508565-01.
What it means
Lennox splits its soft lockouts by what actually ended the sequence, which makes them far more useful than a generic lockout code. E270 is the retry family: the furnace attempted ignition the maximum number of times and no flame current was sensed on any of them. No flame current at all is a different situation from a weak signal. It means either nothing lit, or something lit and the sensing circuit could not see it even slightly. Lennox's steps follow that split — check for proper gas flow, confirm the ignitor is lighting the burner, and check the flame sensor current. The first two ask whether there was a flame; the third asks whether it could have been detected.
Most common causes
- No gas reaching the burners — a closed manual valve, an interrupted supply, or recent work on the gas line.
- An ignitor that is not lighting the burner, whether failed or out of position.
- A gas valve not opening when energised.
- A flame sensor so heavily coated, cracked or mispositioned that it reads nothing.
- A poor chassis ground or reversed line polarity, which prevents rectification entirely.
How to diagnose it
- Confirm the gas is on, including any manual valve at the furnace and at the meter.
- Note whether the burners light at all before shutdown. That single observation splits this code in half.
- Note whether other gas appliances in the house are working, which separates a furnace fault from a supply problem.
- The rest is inside the burner compartment and belongs to a technician.
How to fix it
- Technician work beyond confirming the gas supply.
- Lennox notes the lockout clears when a heat call finishes successfully, so the furnace will retry on its own.
- Stop resetting it repeatedly. Each attempt puts unburnt gas into the heat exchanger before the trial fails.
- Ground and polarity are worth confirming before parts are replaced.
Notes
The difference between E270 and E273 is the difference between never lighting and lighting then losing flame. Same lockout, opposite repairs.
Related
- E273 — Soft lockout — recycles exceeded after flame failure
- E290 — Ignitor circuit fault — failed ignitor or triggering circuit
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.