Lennox furnace E272: Soft lockout — recycles exceeded, pressure switch opened
E272 means the furnace lit successfully, then lost the pressure switch during the run, enough times to exhaust its recycle allowance. The last recycle was caused by the pressure switch opening.
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
A recycle is different from a retry. A retry is a failed attempt to light; a recycle is a run that started properly and was cut short. E272 says the furnace has been lighting fine and then losing proof of draft partway through, repeatedly, until the control gave up. That pattern is characteristic of something that changes while the furnace runs — condensate accumulating, a vent restriction that only matters at temperature, or an inducer that fades under sustained load. Lennox's troubleshooting for this one adds a step the other pressure switch codes do not have: check whether the low pressure switch is stuck closed on a heat call, alongside the usual pressure measurements and vent inspection.
Most common causes
- Condensate building up during the cycle and interfering with the switch or collector box.
- A blocked or slow condensate drain.
- A vent restriction that becomes significant once the system is hot.
- An inducer losing performance under sustained running.
- A low pressure switch stuck closed, which Lennox names specifically for this code.
How to diagnose it
- Note how long the furnace runs before it stops — a consistent interval points at something thermal or accumulating.
- Note standing water near the furnace or a slow condensate drain.
- Check the vent and intake terminations outside.
- Note whether the house gets partly warm before the furnace quits, which confirms it is recycling rather than failing to light.
How to fix it
- Clearing a blocked condensate drain is often the whole repair, and it is the most common cause of this pattern.
- The pressure measurements and the stuck-closed check are technician work.
- The lockout clears when a heat call finishes successfully, so the furnace will try again on its own.
Notes
A furnace showing recycle lockouts is in better shape than one showing retry lockouts — it is lighting correctly. The problem is downstream of ignition.
Related
- E271 — Soft lockout — retries exceeded, pressure switch opened
- E273 — Soft lockout — recycles exceeded after flame failure
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.