Lennox Furnace Error Codes List: Every Code Explained

Every Lennox furnace error code we could verify against Lennox's own documentation — what it means, what usually causes it, and the first fix to try — in one table. Codes differ between model series, so treat your model's tech sheet as the final word.

How to read and retrieve error codes on Lennox furnaces

Lennox boards store a fault history readable through the board display and, on iComfort systems, through the thermostat's alert history — the most reliable way to see intermittent faults that never appear while a technician is watching.

The complete Lennox furnace error code list

How to reset / clear error codes on Lennox furnaces

Lennox furnaces show alphanumeric codes on the board's 7-segment display (and on iComfort thermostats). Most codes clear when the fault condition ends and a successful cycle completes; communication codes (the E2xx family) clear with a power cycle of both the indoor unit and the thermostat once wiring is checked. A recurring code after reset is an active fault.

How to diagnose any Lennox furnace code

Work the problem in this order — and stop at any point where gas, combustion or mains wiring is involved, because those belong to a licensed HVAC technician: (1) record the code exactly: count LED flashes slowly, twice, or photograph the alphanumeric display; (2) check the free things homeowners legitimately own: the thermostat is calling for heat, the furnace power switch and breaker are on, the filter is not clogged solid (a starved furnace overheats and locks out on limit codes), all vents and the return are open, and the condensate drain is not blocked on condensing models; (3) reset once — at the power switch, off for 30 seconds — then watch a full call for heat from the beginning: inducer, ignition, flame, blower, in that order; where the sequence stops is the fault family the code names; (4) a code that returns immediately is an active fault — do not keep resetting a lockout, especially any flame or limit code; (5) everything inside the burner compartment — flame sensor cleaning is the one grey area many manuals allow owners, but gas valves, burners, heat exchangers and control boards are professional work. If you smell gas at any point, leave and call the gas utility, not a helpline.

How Lennox reports faults

Lennox has used two reporting generations. Older boards flash a single LED in patterns counted against the chart inside the blower door. Newer integrated controls show alphanumeric E-codes on a small display and store a history of recent faults that a technician can recall — useful, because an intermittent fault (a pressure switch that fails only on windy days, a flame signal that fades as the sensor oxidises) often appears in the history even when the current call for heat succeeds. The table below covers the E-code generation; for a flashing-LED board, your door chart is the authority for your exact model.

Codes that share a system

Lennox E-codes cluster by the step of the heating sequence they monitor: inducer and pressure-switch codes, ignition and flame codes, limit and rollout codes, blower codes, and communication codes between the thermostat and the control. When two codes appear together, read them as one story — a limit code after a blower code usually means the blower fault overheated the furnace, not that two parts failed at once.

Reading the chart inside the door

On flashing-LED models the chart is glued inside the blower compartment door, and it — not any website — is the authority for your furnace, because Lennox reused flash counts across product generations. Count carefully: the pattern repeats with a longer pause between repeats, flashes within a pattern may mix long and short, and a steady-on or steady-off LED is itself a status (normal operation or no power / board fault, per the chart). Write the count down before resetting anything; a lockout cleared at the switch takes its evidence with it.

Blink codes, display codes and lockouts

Two generations of fault reporting live side by side on modern furnaces. Older and simpler boards report through a single LED: a repeating count of flashes, read slowly against the chart printed inside the blower door — that chart, for your exact model, outranks any list on the internet, including this one. Newer communicating furnaces show alphanumeric codes (the E-series in the table above) and store a fault history a technician can scroll. Both generations share the lockout idea: after a set number of failed attempts at the same step — ignition is the classic — the board stops trying for a period (often an hour, or until power is cycled) instead of cycling forever against a fault that could overheat or flood the burners with unburned gas. A furnace in lockout is not broken by the lockout itself; it is a furnace that has already failed the same step repeatedly and is waiting for someone to find out why.

Furnace codes are also seasonal in a way washer codes are not. The first cold snap produces a wave of ignition and flame codes from furnaces that sat idle all summer — oxidised flame sensors, spider-nested burners, pressure-switch hoses holding condensate from the cooling season. Deep-winter adds frozen condensate lines on high-efficiency models and intake/exhaust terminations blocked by snow or ice, which present as pressure-switch codes. A code that appears once, on the coldest night of the year, and never again has often met its cause already; a code that appears every cycle, in any weather, is a component asking to be tested.

The most searched Lennox furnace codes, in detail

E201 — Communication fault on Lennox communicating (iComfort) furnaces

Lennox's communicating systems (iComfort thermostats with matching furnaces/air handlers) report E201 when the equipment stops communicating on the system's bus — the thermostat can't talk to the indoor unit (or a component has dropped off the bus). Causes are wiring (the 4-wire communicating run), a component without power, or a board fault. Non-communicating Lennox furnaces use LED codes instead, so E201 also tells you which Lennox generation you own.

Most likely cause: Communicating wiring fault — A loose, corroded or damaged conductor in the thermostat-to-unit bus run.

First check: Check the obvious power items first: furnace switch on, breaker on, and the condensate overflow float switch (a tripped float kills the unit's power and looks like a comms fault).

If it keeps coming back: E201 returning with condensate refills points at a slow drain — the comms code is downstream of a drain problem.

Less common and model-specific codes

Search data shows owners also meet these codes on Lennox furnaces: 227, 228, 240, 270, 292, C2, Fixes, Furnace, H1, H2. They are not part of the core code list Lennox publishes for most models — several are series-specific, abbreviated display readings, or codes carried over from a sister platform — so we do not publish meanings for them rather than guess. Treat them by symptom: note what the machine was doing when the code appeared (filling, draining, heating, spinning), run one full power cycle (5 minutes off), and if the code returns, match the symptom to the closest documented family in the table above and check the tech sheet stored inside your machine for the model-specific definition.

Related guides

Facts on this page were checked against manufacturer documentation: www.lennox.com · manuals.plus · manuals.plus · safe-manuals.com