A fault code is the most useful thing a Lennox tells you and the most commonly misread — partly because Lennox uses two completely different reporting systems depending on the equipment generation. This page is the Lennox-specific companion to our general furnace repair service and our Lennox brand overview, and it splits the two contexts so you are not misled.
Two systems, two places to read the code
Be clear which one you have before you read anything:
- Communicating Lennox (Signature and Elite equipment with an iComfort S30 or E30 thermostat): the fault appears as an alphanumeric alert code on the thermostat screen, and the full timestamped history lives under Settings and then Diagnostics. This is the system most newer Lennox installs use.
- Conventional Lennox (older furnaces and air handlers): a diagnostic LED on the control board — usually a pair labeled DS1 and DS2 — flashes the code, read through the inspection port on the lower panel.
The two systems do not share a numbering scheme, so a control-board flash count and an iComfort alert code are read in different places and mean different things. Below, each section is labeled by context.
Conventional control-board LED codes
Older Lennox furnaces use the dual DS1/DS2 LEDs — typically green for normal operation, red for a fault. A slow, steady blink generally indicates a normal call for heat; a repeating flash pattern indicates a specific fault that you count.
Important honesty note: Lennox used several different control boards across furnace models and generations, and the exact number-to-fault map is not uniform between them — a given flash count can mean different things on different boards. The legend printed on the furnace door or in the unit’s manual is the authoritative key for your specific board. The one pattern that is consistent enough to call out is that a limit-circuit fault from overheating (restricted airflow, a clogged filter, a dirty blower) is among the most common things the board flags — and the airflow chain behind it is the same one walked through in our furnace short-cycling guide. Rather than publish a generic flash chart that may not match your board, we read your board’s pattern against its own legend and confirm the fault on the meter.
iComfort S30 alert codes
On a communicating system the iComfort thermostat shows an alphanumeric alert code and logs it with a timestamp. These are the ones we field most, with their Lennox meanings:
| Alert code | Lennox meaning |
|---|---|
| E124 | Thermostat communication failure — equipment lost the thermostat signal for more than ~3 minutes |
| E125 | Control self-check / internal hardware fault (critical) — cycle power, replace control if persistent |
| E200 / E201 | Communication fault between the iComfort thermostat and equipment — usually a C-wire or loose bus connection |
| E227 | Low-pressure switch open — low refrigerant charge (a leak) or a faulty sensor |
| E228 | Low flame-sense signal — a dirty or mispositioned flame sensor, or low gas |
| E311 | Compressor lockout from repeated high-pressure trips — usually a dirty condenser coil or a failing fan motor |
| E380 | Variable-speed (ECM) blower motor fault — motor module on Signature and Elite air handlers |
The communication codes (E124, E200/E201) point at the wiring bus; E227 is a refrigerant-circuit fault that needs gauges; E228 is an ignition/flame fault we confirm with a flame-sense microamp reading; E311 is the coil-and-heat-load lockout covered on our Lennox AC not cooling page. The ignition chain behind a flame-sense alert is on our Lennox furnace not heating page and in our furnace ignitor failure guide.
A note on accuracy: Lennox alert-code lists circulate widely online and not all of them agree — we publish only the codes we can corroborate against Lennox’s own documentation and our own service tickets, and we confirm every one on the meter before naming a part. If your iComfort shows a code not listed here, we read it against the current Lennox alert-code reference on site.
Reading the code is the start, not the fix
Here is the honest part. A code — LED or alert — names a subsystem, not a failed part. An E227 can be a $185 valve-core fix or a coil-replacement conversation; an E311 can be a coil you rinse yourself or a failing fan motor; an E228 can be a $185–$295 flame-sensor clean or a gas-pressure problem. We read the code on arrival, then confirm it on the meter — flame-sense microamps, refrigerant pressures, bus voltage, amp draws — and only then name the part. We do not guess from the code alone, and we do not jumper a safety to force a system to run. The flat $89 diagnostic ($149 after-hours) credits to the repair, so the read-and-confirm step costs you nothing if you proceed.
The SoCal pattern behind the codes
Most of these surface on a schedule. The cooling codes (E227, E311) cluster in the first inland heat waves — a coil that is fine at 80°F cannot reject heat at 104°F in Pasadena or Riverside, so the high-pressure lockout trips. The heating codes (the flame-sense and ignition faults) cluster on the first cold night in November, when an idle furnace fires hard for the first time in eight months and a dust-coated flame sensor or a tired ignitor finally gives out. On the coast in Santa Monica, Manhattan Beach, and Malibu, salt-air corrosion drives communication and electrical faults earlier in the unit’s life. Fall and spring maintenance catch most of these before they become a no-heat or no-cool call.
Lennox diagnostic pricing
Reading and confirming the code is the $89 diagnostic ($149 after-hours), credited to the repair. The repair price follows the cause, flat-rate from our SoCal tickets: flame sensor $185–$295, hot-surface ignitor $245–$485, gas valve $385–$685, integrated control board $480–$950, draft inducer $580–$1,100. A cracked heat exchanger ($1,500–$3,500) is the one fault where we quote replacement against repair and red-tag the furnace if it is leaking. Full furnace table on our Lennox furnace repair page; refrigerant-circuit faults (E227, E311) are priced with the cooling side on Lennox AC not cooling.
iComfort and older Lennox systems
We diagnose both the current iComfort-communicating systems and older conventional Lennox units that report on the control-board LED. For the cooling side of a Lennox system, see Lennox AC repair, and the full lineup on our Lennox brand page.