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.
Where E272 sits in the soft-lockout ladder
The 508565-01 table defines five E27x soft lockouts, and reading them as a set tells you what the control concluded before it gave up. The first two are retry codes — the furnace never lit; the next three are recycle codes — it lit and could not stay running, with the code recording what ended the final attempt:
| Code | Retries or recycles | What ended the last attempt |
|---|---|---|
| E270 | Retries | No flame current ever sensed |
| E271 | Retries | Pressure switch opened |
| E272 | Recycles | Pressure switch opened |
| E273 | Recycles | Flame failure |
| E274 | Recycles | Limit circuit opened |
E272 is therefore the narrowest of diagnoses: ignition is proven good, flame sensing is proven good, and the thing that keeps failing is proof of draft after the furnace is hot and running. All five clear the same way — when a heat call finally completes successfully — so a furnace that struggles through one full cycle wipes its own lockout, which is why the stored code history matters more than what the display shows right now.
What the fix costs
The happy version of this repair is nearly free: a condensate drain cleared of sludge, which is the most common reason a running condensing furnace progressively loses its draft signal. The paid versions, per the repair cost guide: pressure switch work runs $150–400 — with the guide's own caution to check for a blocked flue before condemning the switch — and an inducer that fades under sustained load is the expensive suspect at $300–900, with brand parts availability driving the spread. Getting the cheap cause ruled out first is legitimate; a technician who quotes an inducer without checking the drain and vent has skipped the order of operations Lennox's own checklist implies.
DIY or call a pro
The homeowner jobs for this code are the accumulation checks, because E272 is a fault that builds while the furnace runs: look for standing water at the furnace or a condensate drain that trickles rather than flows, and walk outside to check the intake and exhaust terminations for snow, leaves or ice — all safe, all power-off-not-required, and together they cover the most common causes. Everything with a manometer — measuring switch operating pressure in inches of water column, and Lennox's E272-specific check of whether the low pressure switch sticks closed on a heat call — is technician work. The hard line: never jumper the pressure switch to keep the furnace running through the lockout. This switch is what proves the flue is actually carrying combustion gases out of the house while the furnace is hot.
What this looks like
From the outside, this usually shows up as the furnace starts and stops in short bursts — that walkthrough covers what to check in order, and when it stops being a homeowner job.