What does Lennox E274 mean?

E274 is a soft lockout on Lennox communicating furnaces. It fires when the primary limit switch opens and stays open for more than three minutes across multiple ignition attempts, exceeding the maximum retry count.

What does Lennox E250 mean?

E250 indicates the primary limit switch circuit is open on a Lennox communicating furnace. The limit switch is a thermal safety device that opens when the heat exchanger gets too hot. If the switch does not close within three minutes, the furnace enters a 60-minute soft lockout (Watchguard mode).

What does Lennox E275 mean?

E275 is a soft lockout triggered when the Lennox communicating furnace detects flame out of sequence — specifically when a flame signal disappears after being sensed out of sequence (code E241 condition). The furnace enters Watchguard mode.

How do I access diagnostic codes on a Lennox iComfort thermostat?

On the Lennox iComfort S30 or E30 thermostat, navigate to Settings > Advanced Settings > Dealer Controls > Diagnostics. Active faults are displayed with descriptions. You can also run a system test from this menu to verify all components are operational. Ensure the thermostat firmware is up to date before diagnosing software-related issues.

How do I check refrigerant charge on a Lennox XC21 system?

The Lennox XC21 uses R410A and requires charging by weighing refrigerant, not by superheat/subcooling alone for the initial charge. Use the charging chart on the inside of the access panel as a reference. Target 10-12°F subcooling at the condenser outlet and 8-12°F superheat at the evaporator outlet under rated conditions.

What does Lennox error code E201 mean on an SL280 or SLP99 furnace?

E201 indicates the integrated furnace control (IFC) has lost communication with the variable-speed indoor blower motor. The communicating ECM blower exchanges digital signals with the IFC; when that link drops, the board logs E201 and disables heating to prevent unventilated heat buildup. Cycle furnace power for 60 seconds to clear transient dropouts; if E201 returns, inspect the multi-pin communication harness between the IFC and the blower-motor module for loose pins, damaged insulation, or moisture, and check the IFC's 3-amp or 5-amp fuse. Persistent faults usually mean an ECM motor module failure that requires replacement and capacity-code reprogramming.

What does E290 mean on a Lennox furnace and how do I fix it?

E290 is an ignitor circuit fault. The IFC monitors the hot-surface ignitor before and during warm-up; an open or out-of-range resistance reads E290 and forces a soft lockout for about an hour. Power down the furnace, disconnect the ignitor harness, and measure resistance across the ignitor terminals — 39 to 70 ohms is acceptable, OL confirms a failed silicon-nitride element. Inspect for visible cracks or carbon tracking, check harness continuity from the IFC ignitor output to the ignitor connector, and verify 120 V AC is present at the ignitor terminals during the warm-up period. If voltage is missing, the IFC's ignitor triggering circuit is faulty; if voltage is present and resistance is in spec but E290 returns, a board-level sensing circuit failure is the most likely cause.

HVAC

Lennox error codes, decoded.

Look up any Lennox fault code below. Each one is grounded in Lennox's own service documentation — the meaning, the symptoms, the causes, and the steps to clear it.

Quick answer

Lennox communicating furnaces and air handlers display three-digit E-codes (E200 series for ignition and pressure-switch faults, E270/E290 for ignitor and flame issues, E274/E292 for blower and limit faults, E370/E402 for accessory interlocks) on the iComfort S30 / E30 / M30 thermostat. The same code book is shared across Aire-Flo, Concord, and Ducane (Lennox-owned sister brands).

By Octavian Ghindea

Co-founder & CTO · Reviewed May 2026

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Lennox sits in our HVAC coverage. Every page here is transcribed from the manufacturer's manuals, not scraped from forums.

What error codes does Lennox display?

Tap a code for the full breakdown — meaning, symptoms, causes, and fix steps.

E274

Diagnostic Codes/Status of Equipment Soft lockout - Exceeded maximum number of A

E250

. recycles. Last recycle failed due to the limit circuit opening or limit remain

E275

E276 E290 E291 E292 Soft lockout - Flame sensed out of sequence from code 241 fa

E294

Combustion air inducer motor amp draw is too Check combustion blower bearings, w

E295

Indoor blower motor temperature is too high. Indoor blower motor over temperatur

E310

Discharge error sensor failure - No error if Discharge air temperature(DATS) out

E311

Heat rate reduced to match indoor blower air Furnace blower in cutback mode due

E312

Restricted air flow in cooling or continuous fan Restricted airflow - Indoor blo

E313

Indoor or outdoor unit capacity mismatch. Incorrect Indoor /outdoor capacity cod

E401

communicating outdoor unit (Dual fuel module required for heat pump application)

E402

LSOM - Outdoor unit system pressure trip. Compressor ran over 18 hours in air co

E403

LSOM - Compressor short-cycling (Running less than 4 minutes). Outdoor unit pres

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