Lennox SLP98UHV Error Code E 270: Soft Lockout - No Flame Sensed
What Does Code E 270 Mean?
The E 270 fault on the Lennox SLP98UHV is a soft lockout that occurs after the control exceeds its maximum number of ignition retries with no flame current sensed. The furnace tried to light several times, the flame sensor never confirmed a flame, and the SureLight control shut the sequence down. Being a soft lockout, it clears once a later heat call completes successfully, unlike the E 200 hard lockout that has to be cleared deliberately.
During each attempt the board energizes the hot surface ignitor, opens the gas valve, and waits for the flame sensor to prove flame. If flame is not sensed within the allowed window, the valve closes and the furnace retries; after the retries are used up it lands in E 270. Because no flame was ever confirmed, the cause is somewhere in the ignite-and-prove chain rather than a flame that started and dropped out (that pattern points instead to E 273).
There are two broad categories. Most commonly the burners are actually lighting but the flame sensor is too dirty to detect the flame, which ties E 270 to the same weak-signal condition behind E 240 (low flame current). Alternatively the burners are not lighting at all, which points to a gas supply problem (closed manual valve, empty propane tank, or utility interruption), a failed hot surface ignitor (see E 207), or a gas valve fault. Whether the burners visibly light before shutdown is the key clue a technician uses to separate the two.
What You'll Notice
- The furnace tries to light several times, then gives up and stops — no heat
- You hear repeated ignition attempts (inducer, click, brief glow) that never sustain
- The burners may light for a moment, then the flame goes out and the unit quits
- No warm air at the registers even though the thermostat is calling
- The 7-segment display shows E 270 in the fault history
Common Causes
How This Is Diagnosed
A technician first establishes whether the burners are actually lighting. If they light but the unit still locks out, the flame-sensing side is the focus — they measure the flame sensor's microamp signal and clean the rod with a Scotch-Brite pad if it is coated, then confirm the furnace ground, mirroring the E 240 diagnosis.
If the burners are not lighting, they work back through the ignition chain: confirming gas is present and the manual valve is open, checking the hot surface ignitor's resistance and glow, and verifying the gas valve is opening on command. The specific failed link determines the repair.
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 makes repeated ignition attempts but never produces sustained heat
- The burners do not light at all (no flame visible through the sight glass)
- The ignitor does not glow during the ignition sequence
- Other gas appliances work but the furnace will not light
- You smell gas near the furnace while it is trying to ignite
Frequently Asked Questions
Is it safe to keep resetting the furnace on E 270?
Repeatedly forcing ignition attempts is not a good idea, especially if the burners are not lighting, because it can send unburned gas through the system. The soft lockout is designed to stop that. It is better to have a technician find why flame is not being confirmed than to keep cycling power.
The burners light for a second then go out — what does that mean?
That pattern usually means the burners are igniting but the flame sensor can't confirm the flame, most often because the sensor rod is dirty. It's the same weak-signal issue behind E 240. A technician can measure and clean the sensor and check the ground to restore reliable detection.
Could a simple gas supply issue cause E 270?
Yes. A closed manual gas valve, an empty propane tank, or a utility interruption will keep the burners from lighting and can drive the furnace into E 270. Checking whether your other gas appliances work is a useful clue, but the furnace itself should be verified by a technician.
✓ Verified against manufacturer service manual — March 2026