HeatingCodesLennox furnace code E250: limit switch circuit open (and E274)
What E250 means
Lennox's diagnostic code table for the SL280DFV lists E250 as Limit switch circuit open. The limit switch protects the heat exchanger from overheating. When it opens, the furnace stops burning gas. The corrective action in the manual says to "check for proper firing rate on furnace," "ensure there is no blockage in heater" and "check for proper air flow."
The manual also says that if the limit does not close within 3 minutes, the unit will go into a 1-hour soft lockout. E250 "resumes normal operation after fault is cleared."
E250 versus E274 and E200
| Code | Meaning (per Lennox) | Clearing |
|---|---|---|
| E250 | Limit switch circuit open | Resumes normal operation after the fault is cleared. Becomes a 1-hour soft lockout if open longer than 3 minutes. |
| E274 | Soft lockout: last recycle failed because the limit circuit opened, or the limit remained open longer than 3 minutes | 1-hour soft lockout. Check firing rate and airflow and check for blockage. Clears when the heat call finishes successfully. |
| E252 | Discharge air temperature too high (gas heat only) | Check temperature rise, airflow and input rate. Cleared when the heat call is finished. |
| E200 | Hard lockout: rollout circuit open or previously open | Correct the cause of the rollout trip, or replace the flame rollout switch, then test furnace operation. |
The rollout code E200 is the one to take most seriously. A flame rollout switch trips when flames come out where they should not, and it should not be reset without finding the reason.
What usually causes a limit trip
Lennox's text points at firing rate, blockage and airflow. Airflow problems are the most common category for homeowners to fix: a clogged filter, closed supply registers, a blocked return grille or a duct problem all raise the temperature in the heat exchanger. A technician checks the firing rate (gas input) and the heat exchanger itself.
Safe homeowner checks for Lennox furnace code E250
- Turn the thermostat to offLet the furnace cool. The limit usually closes again once the heat exchanger cools down.
- Replace a dirty filterA clogged filter restricts airflow across the heat exchanger. Install a clean filter of the right size.
- Open and clear registersMake sure supply registers and return grilles are open and not covered.
- Restart and watchSet the thermostat to heat. If E250 or E274 returns, stop and call a heating technician.
Frequently asked questions
How long is the Lennox 1-hour soft lockout?
Lennox lists E274 as a 1-hour soft lockout, and says it clears when the heat call finishes successfully.
Can E250 be a dirty filter?
Yes, restricted airflow is a standard cause of an open limit, and Lennox tells the technician to check airflow. A filter is the first thing to check. If a new filter and open registers do not stop the code, there is another cause.
Does E250 mean my heat exchanger is bad?
Not by itself. It means the limit circuit opened. The cause can be airflow, firing rate, blockage or a defective switch. A technician finds which.
Sources
- Installation Instructions 508246-01 (04/2024): SL280DFV Elite Series gas furnace, Integrated Control Diagnostic Codes (Lennox) Covers: Lennox SL280DFV variable-capacity condensing gas furnaces with the integrated control described in the document. Other Lennox furnace lines can use different code sets.
Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.