Lennox SLP98UHV Error Code E 271: Soft Lockout - Pressure Switch Opening
What Does Code E 271 Mean?
Error code E271 on the Lennox SLP98UHV indicates a soft lockout after exceeding the maximum number of retries, with the last retry failing because the pressure switch opened. The pressure switch initially closed (allowing the ignition sequence to begin) but then opened during or just before ignition, aborting the process. After too many failed attempts, the furnace entered soft lockout.
This code differs from E223 (pressure switch failed to close) because in E271, the switch did close initially but could not stay closed. This suggests an intermittent or marginal draft condition rather than a complete blockage. The lockout clears when a subsequent heat call completes successfully.
The most common cause is a partial blockage in the exhaust vent — enough airflow gets through for the switch to close initially, but not enough to maintain consistent draft during the ignition sequence. Wind gusts, partial ice buildup, or debris that shifts position can all cause this intermittent behavior. Other causes include a pressure switch hose with a small leak, condensate partially blocking the inducer, or a weak inducer motor.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked exhaust vent causing pressure switch to open during operation | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- E271 returns after clearing all visible vent obstructions
- The problem only occurs during windy conditions (may need a vent wind guard)
- You find water in the pressure switch hose or inducer housing
- The inducer motor sounds weak or inconsistent
- The condensate drain is difficult to access or repeatedly clogs
✓ Verified against manufacturer service manual — March 2026