The short answer
A Lennox error code in Northern Virginia tells you which safety tripped, not which part failed. On newer Lennox gas furnaces it’s an E and three digits on the control board, like E250 or E270. On older Merit furnaces it’s a red light that blinks a count. On an S30 or S40 thermostat it’s an alert number with a priority. A few are five-minute fixes you can do yourself: a filter, a switch, a door panel. Most mean a part needs testing. Two, E200 and E150, mean shut it off and call.
If you smell gas, skip all of it. Leave the house and call the gas company and 911 from outside. If a carbon monoxide alarm is going off, get everyone out first (what to do when the CO alarm sounds).
Where to find the code on your Lennox
On the furnace’s control board. The SL280V, EL296V, SLP99V and the newer K furnaces show an E code on a small display on the board. Read it through the window in the lower door if yours has one. The lower door pushes a safety switch, so taking it off cuts the power and can clear the display. Take a photo of the code before you reset anything. A reset can clear what’s showing, and that number saves the tech time and you money.
A red light that blinks. Merit furnaces like the ML180UH, ML180UHE, ML195UH and ML296UHV blink a count instead. Count the flashes, then check the model number on the sticker inside the door, because the same count means different things on different Merit furnaces.
On the thermostat. The S30 and S40 show an alert number and a priority. The same numbers you’d see on the board show up there, and the outdoor unit reports in too. More on the S40 Service Urgent alert.
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Soft lockout or hard lockout
Lennox uses two kinds of lockout. A soft lockout waits an hour, then tries again on its own if the thermostat still wants heat. A hard lockout stays off until someone turns the power off and back on. Resetting once is fine, and sometimes it gets you through the night. Resetting over and over only hides the reason, and with a rollout switch it can be dangerous.
Lennox furnace E codes
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| Code | What Lennox says | What it usually means for you |
|---|---|---|
| E105 | Device communication problem | The furnace can’t hear the thermostat or the outdoor unit. Usually wiring or electrical noise. Clears when they talk again. |
| E115 | Low 24 volt control power | The board needs 18 to 30 volts. A tech checks the transformer and anything wired into it. |
| E180 | Outdoor air temperature sensor failure | The sensor or its wire. The heat still runs. |
| E200 | Hard lockout, rollout circuit open or previously open | Flames came out of the burner area. Leave it off and call. E200 explained |
| E201 | Indoor blower communication failure | The board can’t talk to the blower motor. Can show after a power outage. Blower codes |
| E202 | Indoor blower motor mismatch | The motor doesn’t match the size the board is set for. A setup fix. |
| E203 | Appliance capacity or size not programmed | Usually a board that was swapped and never set up. |
| E204 | Gas valve miswired | A wiring fix at the gas valve. Call. |
| E207 | Hot surface ignitor sensed open | The igniter is broken. Ignition codes |
| E223, E224, E225, E227, E228 | Pressure switch failed open, stuck closed, or the inducer couldn’t calibrate | Venting, the inducer or the switch. Pressure switch codes |
| E240 | Low flame current, run mode | Usually a dirty flame sensor. E240 explained |
| E241 | Flame sensed out of sequence, flame still present | Flame where there shouldn’t be any. Turn the gas to the furnace off and call. E241 explained |
| E250 | Limit switch circuit open | It ran too hot. Check the filter first. E250 explained |
| E270 | Soft lockout, exceeded maximum retries, no flame current sensed | It tried to light and never saw a flame. E270 explained |
| E271 | Soft lockout, last retry failed because the pressure switch opened | Venting or the inducer. Pressure switch codes |
| E274 | Soft lockout, last recycle failed on the limit, or the limit stayed open over 3 minutes | E250 that didn’t clear. E250 and E274 |
| E290 | Ignitor circuit fault, failed ignitor or triggering circuitry | The igniter or the board that powers it. Ignition codes |
| E292 | Indoor blower motor unable to start | A seized motor or a jammed wheel. E292 explained |
| E311 | Heat rate reduced to match indoor blower air flow | Not enough air, so the furnace turned its own heat down. Filter, vents, ducts. |
| E313 | Indoor or outdoor unit capacity mismatch | A setup code on communicating systems. |
| E370 | Interlock switch sensed open for 2 minutes | The lower door isn’t seated. Push it closed. |
| E150 | Refrigerant leak detected | The leak sensor at the coil found refrigerant. E150 explained |
| E151 | Refrigerant leak detector sensor fault | The sensor itself failed. Leak sensor codes |
Some charts online give E200 through E203 different meanings. The ones here are from Lennox’s own service manuals for the SL280, EL296 and SLP99 furnaces.
Merit furnaces with a red light
The count means different things depending on the furnace. Match your model before you trust any chart, including ours.
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| What tripped | ML180UH and ML195UH | ML296UHV | ML180UHE |
|---|---|---|---|
| Flame sensed with the gas valve off | 1 flash | 1 flash | 12 flashes |
| Pressure switch open with the inducer running | 3 flashes | 3 flashes | 9 flashes |
| Limit switch open | 4 flashes | 4 flashes (limit or rollout) | 7 flashes |
| Rollout switch open | 5 flashes | 4 flashes (limit or rollout) | 8 flashes |
| Burners won’t light, lockout | 7 flashes | 7 flashes | 5 flashes |
| Low flame signal | Not on this board | Not on this board | 4 flashes |
The full chart for each Merit model is in Lennox furnace flashing red light.
Lennox AC and heat pump codes
The outdoor unit reports through the S30 or S40 as a 400-series alert.
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| Alert | What Lennox says | Priority |
|---|---|---|
| 400 | Compressor internal overload tripped | Service Soon |
| 401 | Compressor long run cycle, over 18 hours on one call, or low system pressure | Information |
| 403 | Compressor short-cycling, ran less than 3 minutes | Service Soon |
| 404 | Compressor rotor locked | Service Urgent |
| 411 | Low pressure switch lockout, opened 5 times in one call | Service Urgent |
| 413 | High pressure switch lockout, opened 5 times in one cooling call | Service Urgent |
| 414 | High discharge line temperature | Service Soon |
| 426 | Excessive inverter alarms | Service Urgent |
What each one usually is, and what to check: Lennox AC and heat pump error codes.
S30 and S40 thermostat alerts
Service Urgent, in Lennox’s words, is a “no heat, no cool or no ventilation status.” The ones we see most: 31 (lost communication with a device for more than 3 minutes), 603 (the float switch in the drain pan opened), and 71511 (indoor duct or filter blockage). A full drain pan can kill the thermostat’s power and look like a dead system. Every common S40 alert.
No code, or a different problem?
Plenty of Lennox trouble never shows a code. Pick the one that sounds like yours:
- How to reset a Lennox furnace: and the buttons to skip
- Lennox furnace not igniting: clicks, glows, never lights
- Lennox furnace blowing cold air: six reasons, most of them simple
- Lennox furnace blinking green light: which light it really is
- Lennox E228 and E229: the pressure switch calibration codes
- Lennox AC not cooling: seven checks, then the usual fixes
- Lennox thermostat reset: S40, S30, E30 and M30 steps
- Lennox thermostat not working or blank: what to check first
Another brand of furnace or AC? Codes from every brand, in one place: furnace and AC error codes.
What you can check yourself
The filter. A packed filter sets off E250, E274 and E311. Change it, wait a few minutes, try again. Heavy pleated filters can choke a furnace too (which filter to buy).
The furnace switch and breaker. The switch near the furnace looks like a light switch. A tripped breaker sits in the middle. Reset it once; if it trips again, leave it off.
The lower door. If it isn’t pushed all the way in, you get E370 and nothing runs.
The drain. High-efficiency Lennox furnaces make water. A clogged drain or a full condensate pump stops the heat on purpose (clogged furnace drain).
The vent pipes outside. If your furnace vents through white plastic pipe, make sure snow, leaves or a nest aren’t blocking where they end outside.
Never jump a safety switch to get heat back. Every one of them is there to stop a fire or carbon monoxide.
What the usual Lennox fixes cost
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| The fix | Our price |
|---|---|
| Flame sensor cleaned | $95 to $180 |
| Condensate drain cleared, trap and switch added | $175 to $420 |
| Igniter or flame sensor replaced | $240 to $410 |
| Blower wheel pulled and cleaned | $300 to $440 |
| Control board replaced | $550 to $1,180 |
| Blower motor replaced | $670 to $2,400, most around $1,500 |
The diagnostic is a flat $99. Pressure switches, limit switches, rollout switches and gas valves get priced in writing once we’ve tested them, before any work starts.
If the repair is a big one on an older furnace, get a second look before you spend it. Our free second opinion costs you nothing, and the estimator shows what a new system costs with $1,500 off already in the price. Thinking about brands? Lennox vs Trane lays out the difference.
The system we put in first
Built to take a beating. Put in by our crew.
Heat lamps, snow and rain on one outdoor unit: that’s Trane’s own film. We’re a Trane Comfort Specialist, on Trane’s own dealer locator, and when you pick a Trane, our crew puts it in.
Films: Trane’s own.
Call or book a Lennox repair
Call (703) 997-9757. We answer day or night. Or book online and pick a time. The diagnostic is a flat $99, and you see the repair price in writing before we touch anything. Furnace running fine and you want to keep it that way? Book the $67 heating check from goswiftpro.com/cookiesoffer (book by November 30) and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276. More on Lennox repair in Northern Virginia.
Questions people ask
What does E250 mean on a Lennox furnace?
The limit switch circuit is open: the furnace got too hot inside and shut the burners off. A dirty filter or blocked airflow is the usual cause. If the limit stays open more than 3 minutes, the furnace goes into a one-hour soft lockout.
How do I reset a Lennox furnace error code?
Photo the code first, then turn the furnace switch off, count to ten, and turn it back on. A soft lockout also clears itself after an hour if the thermostat still calls for heat. If the same code comes back, the reason is still there, and resetting again won’t fix it.
Where do I find the error code on my Lennox furnace?
Newer Lennox gas furnaces show an E code on the control board display behind the lower door. Merit furnaces blink a red light. If you have an S30 or S40 thermostat, the code shows there as an alert.
What does Service Urgent mean on a Lennox thermostat?
Lennox uses it for a no heat, no cool or no ventilation status. Note the alert number on the pop-up and check the filter and the condensate drain. If those are fine, call a technician.
Is a Lennox E200 code dangerous?
It can be. E200 is a hard lockout because the flame rollout circuit opened, which happens when flames come out of the burner area, often from a blocked vent or a cracked heat exchanger. Leave the furnace off and have it checked.
