Lennox furnaces run a built-in diagnostic system that reports faults when the furnace shuts down for safety. On newer models such as the SL280 and EL296, the control board has a small digital display that shows E-codes. This guide covers the common codes so you can understand the message before calling a technician.
How to Read Lennox Error Codes
On Lennox furnaces with a digital display, the code appears on the control board display, usually visible through a window in the blower door. In idle mode the display shows a blinking decimal point. When a fault occurs, the display shows an E-code such as E250. Older Lennox models use different LED patterns, and codes can vary by model and control board, so the chart inside your furnace door or the installation manual is the authoritative reference.
Common Lennox Error Codes
These codes are taken from the Lennox SL280 installation instructions. Codes on other models may differ.
| Code | Fault Description | Likely Cause | DIY or Call? |
|---|---|---|---|
| E200 | Hard lockout: rollout circuit open | Flame rollout from a blocked flue, cracked heat exchanger, or combustion problem | Call immediately: possible CO risk. Do not reset |
| E207 | Hot surface ignitor sensed open | Failed ignitor or ignitor wiring | Call technician |
| E223 | Low pressure switch failed open | Blocked vent or intake, or combustion air inducer problem | Check outdoor vent pipes for snow or ice; call if clear |
| E225 | High pressure switch failed open | Blocked vent or intake, or combustion air inducer problem | Check outdoor vent pipes for snow or ice; call if clear |
| E240 | Low flame current | Dirty or failing flame sensor, or poor grounding | Call technician |
| E241 | Flame sensed out of sequence | Possible gas valve leak | Gas safety issue: turn the furnace off and call immediately |
| E250 | Limit switch circuit open | Restricted airflow: clogged filter, blocked registers, or blower problem | Replace filter first; call if it persists |
| E270 | Soft lockout: too many ignition retries, no flame sensed | Gas supply, ignitor, or flame sensor problem | Confirm the gas valve is open; call if it returns |
| E290 | Ignitor circuit fault | Failed ignitor or ignitor circuit | Call technician |
The Two Most Common Lennox Fault Codes in Ontario
E250: Limit Switch Open (Overheating)
This is the most common Lennox fault call we receive across the GTA. The furnace overheats and the limit switch shuts off the burners. The furnace will often restart once it cools, then shut down again, leading to an on-again-off-again heating cycle.
- Step 1: Turn off the furnace and check the air filter. A filter clogged with dust is the most common cause of limit trips.
- Step 2: Walk through your home and confirm all supply registers and return air vents are open and unblocked by furniture.
- Step 3: If the filter is clean and registers are clear, check that the blower fan runs continuously. If it runs briefly then stops before the burners shut down, the blower motor may be failing.
- Step 4: If the issue continues after changing the filter, call EcoFrost. Repeated limit trips put stress on the heat exchanger.
E270: Ignition Lockout
The second most common fault in Ontario, especially after a season of heavy use. The furnace tries to light several times, does not sense a flame, and goes into a soft lockout for safety.
- Common cause: a dirty flame sensor. The flame sensor is a thin metal rod that confirms gas is actually burning. A coating of oxidation or debris prevents it from detecting the flame.
- Another common cause: a failed hot surface ignitor. The ignitor glows orange before ignition. If it does not glow, the ignitor has likely burned out.
- Less common: low gas pressure due to a partially closed shut-off valve or supply issue.
- What you can do: confirm the gas valve is open and power-cycle the furnace once. Flame sensor cleaning and ignitor replacement are technician tasks, because they mean working inside the burner compartment.
E200 Rollout Lockout: The One You Should Never Ignore
E200 means the flame rollout circuit is open. A rollout switch trips when flames roll out of the burner area instead of staying inside the combustion chamber. This can indicate a blocked flue pipe, a cracked heat exchanger, or improper combustion.
How to Reset Your Lennox Furnace After a Fault Code
For airflow and ignition lockouts (such as E250 or E270), you can attempt one reset after addressing the likely cause. Set the thermostat to OFF, wait 30 seconds, then set it back to HEAT with a setpoint above room temperature. The furnace will attempt a new startup sequence. If the same code returns, the underlying problem has not been resolved and continuing to reset without a repair can damage components. Never reset after a rollout or flame-out-of-sequence code.
Ready to take the next step?
Book a Lennox Furnace DiagnosticWhen to Call a Technician Instead of Resetting
- E200 or E241: rollout or flame sensed out of sequence. Do not reset.
- E270 that returns within one heat cycle after resetting: ignitor or gas supply needs professional diagnosis.
- E250 that returns immediately after changing the filter: blower motor or airflow issue.
- Any code accompanied by a burning smell. For a gas smell or a CO alarm, leave the home first and call Enbridge Gas (1-866-763-5427) or 911 from outside.
- Error codes on a furnace older than 15 years: repair cost vs. replacement value should be assessed.
?Frequently Asked Questions
Where do I see the error code on my Lennox furnace?
My Lennox furnace shows E250 but the filter is clean: what now?
Can I reset a Lennox furnace lockout myself?
What does a blinking decimal point mean on a Lennox furnace display?
How much does Lennox furnace repair cost in the GTA?
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