Lennox SLP98UHV Error Code E 271: Soft Lockout - Pressure Switch Opening
What Does Code E 271 Mean?
A soft lockout is what the SureLight Variable Capacity Integrated Control does after it has retried the ignition sequence too many times and the final retry failed for the same reason each time. In the case of E271, that reason is a pressure switch that opened when it should have stayed closed. The switch closed at the start (allowing the sequence to begin), then opened during the trial for ignition, and after enough repeats the control stopped trying and declared a soft lockout.
This behavior is different from E 223, where the low-fire pressure switch never closes in the first place. In E271 the switch did prove draft momentarily but could not hold it, which usually indicates a marginal or intermittent draft condition rather than a total blockage. Because the SLP98UHV is a modulating furnace that must prove draft as it moves between firing rates, a draft that is only borderline adequate will close the switch briefly and then drop below the trip point, producing exactly this open-during-run pattern. The manual points to the E 223 troubleshooting path for this code, since both trace back to how well the vent and inducer maintain pressure.
Common underlying causes include a partial obstruction in the exhaust vent that lets just enough air through to close the switch initially, a pressure-sensing hose with a small crack or trapped condensate, a weakening combustion-air inducer motor, or wind gusts disturbing the draft at the vent termination. A soft lockout typically clears once a later heat call completes successfully, but it will keep returning until the marginal draft condition is corrected.
What You'll Notice
- The furnace tries to light, runs briefly or not at all, then locks out with E 271
- No heat, with the 7-segment display showing E 271
- The problem is worse in windy weather or during cold snaps
- You hear the inducer start each attempt but the burners never establish a steady flame
- The furnace works intermittently — fine on some cycles, locked out on others
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked exhaust vent causing pressure switch to open during operation | Most common | ✗ Call a pro → |
How This Is Diagnosed
Because E271 signals a draft that closes the switch and then loses it, a technician's first goal is to find what is making the draft marginal rather than absent. A homeowner-safe check you can do first is to inspect the exhaust and intake vent terminations outside for partial blockages — a ridge of ice, drifting snow, leaves, or a nest being built — since these often let the switch close briefly before draft collapses.
The remaining steps are for a technician. They inspect the full vent run for sags, restrictions, or sections that trap condensate, examine the pressure-switch hose for cracks or water, confirm the inducer motor spins up strongly and draws normal current, and measure the operating draft pressure in inches of water column against the switch specification. Because the switch is closing and then opening, they pay particular attention to conditions that cause pressure to fluctuate near the trip point rather than a hard, constant blockage.
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:
- E 271 returns after you have cleared all visible obstructions from the outdoor vent and intake
- The lockout appears mainly during windy conditions
- You find water or a cracked hose at the pressure switch
- The inducer motor sounds weak, uneven, or louder than usual
- The furnace alternates between working normally and locking out
Frequently Asked Questions
What is the difference between E 271 and E 223?
E 223 means the low-fire pressure switch never closed to begin with, so ignition could not even start. E 271 means a pressure switch did close and prove draft briefly, then opened during the attempt, and the furnace locked out after several repeats. E 271 usually points to a marginal or intermittent draft rather than a complete blockage.
The furnace locked out but now it is running again — is it fixed?
A soft lockout can clear on its own once a later heat call succeeds, so occasional recovery is expected. That does not mean the cause is gone. If a marginal draft condition remains, E 271 will return, often on the coldest or windiest days when you most need heat, so the underlying issue should still be diagnosed.
Could wind really cause this code?
Yes. On a high-efficiency furnace, gusts hitting the vent termination can momentarily disturb the draft enough to open the pressure switch. If E 271 tends to appear during windy weather, a technician may look at the vent termination and whether a wind guard or design change is warranted.
✓ Verified against manufacturer service manual — March 2026