Lennox E272 Error Code

What does Lennox E272 mean?

E272 is a soft lockout triggered when the low-pressure switch has opened repeatedly during the run period — exceeding the maximum allowed number of mid-cycle drop-out events. Unlike E271 (pre-ignition), E272 occurs while the furnace is actively heating and losing draft intermittently. The board enters Watchguard mode to prevent repeated short-cycling on a marginal draft condition.

Symptoms

• Furnace lights and runs for a period, then shuts down mid-cycle and logs E272.
• Alert occurs more frequently during cold outdoor conditions or after extended run times.
• Inducer runs but low-pressure switch drops open during the heating cycle.
• E227 faults appear in the fault history prior to the E272 soft lockout.

Common causes

• Partially blocked vent pipe where draft is adequate at startup but degrades as the heat exchanger warms.
• Condensate trap draining slowly and backing water into the inducer housing during extended heating cycles.
• Inducer motor capacitor failing under thermal load — capacitor performs adequately cold but weakens as temperature rises.
• Kinked or partially collapsed pressure switch hose that allows initial pressure to pass but restricts flow during sustained operation.

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Diagnostic steps

1. Reset the lockout and reproduce the fault

   Power cycle the furnace to clear the Watchguard. Run the furnace on a long heating call and monitor whether the low-pressure switch drops open after several minutes of run time — this confirms the fault is thermal or drain-related.

2. Inspect vent pipes during and after operation

   Check exhaust and intake PVC for ice buildup at terminations that develops as warm exhaust gas exits and freezes. Clear ice at the termination and evaluate whether a screen is needed to reduce ice formation.

3. Flush and clear the condensate drain during operation

   Pour water into the condensate trap while the furnace is running. If the trap overflows into the inducer housing, the drain is backing up during operation and is causing the draft disruption.

4. Inspect pressure switch hose under operating conditions

   With the furnace running, feel the pressure switch hose for collapse under sustained draft pressure. Replace any hose that deforms during run.

5. Test inducer motor capacitor under load

   Allow the furnace to run until E272 occurs. Immediately check the inducer run capacitor with a capacitance meter while still warm. Capacitance significantly below the rated µF value confirms thermal degradation.

When to call a professional

Diagnosing an intermittent draft fault that only appears under thermal load requires sustained monitoring with a manometer connected to the inducer housing during a full heating cycle. A licensed technician can monitor inducer performance throughout the cycle, evaluate condensate trap drainage rate under load, and confirm whether the inducer motor requires replacement.