Lennox Furnace Code E250: Limit Switch Open Fix & Cost

Last updated Sep 25, 2026 · By fixme.vip Editorial

Lennox furnace code E250: what it means

On a Lennox board that reports it, Code E250 indicates the limit switch circuit is open — the primary limit has tripped. The limit switch is a safety device mounted near the heat exchanger that monitors cabinet temperature. When it senses the furnace is running too hot, it opens the circuit and shuts off the gas valve to prevent damage to the heat exchanger and surrounding components.

An open limit almost always points to restricted airflow or overheating — the furnace is producing heat faster than the blower can move it out into the house. The code is telling you why the furnace shut down, not that the switch itself is bad — most of the time the switch is doing its job.

Check the code against your own furnace’s literature first. Lennox uses more than one alert-numbering scheme across its product lines, and the same number does not necessarily carry the same meaning on a legacy two-digit LED SureLight board, on an alphanumeric SureLight unit controller, and on an iComfort-communicating system. The diagnostic legend inside the blower-compartment door and the service manual for your exact model number are the authority for your unit. If your literature defines E250 differently, follow your literature rather than this page.

Whatever the label, a tripped limit is a pro-level fault, because the underlying cause frequently lives inside the cabinet (blower, wiring, or the limit itself). Homeowners can safely rule out a handful of airflow issues first, described below.

Lennox furnace code E250: common causes, ranked by probability

1. Dirty or clogged air filter — the number-one cause. A restricted filter chokes return airflow and lets heat pile up until the limit trips.
2. Blocked or closed supply/return registers — too many closed vents, blocked returns, or furniture over grilles reduce airflow the same way a dirty filter does.
3. Dirty blower wheel or failing blower motor — buildup on the blower wheel or a weak/failing motor moves less air, causing overheating.
4. Restricted or collapsed ductwork — undersized, crushed, or disconnected ducts starve the system of airflow.
5. Blower running too slow or wrong speed setting — an incorrect blower speed setting after a service call can under-move air on high fire.
6. Failed or open limit switch — the switch itself can fail open even when temperatures are normal.
7. Loose or damaged wiring to the limit — a broken wire, corroded terminal, or loose connector opens the circuit.
8. Dirty or partially blocked heat exchanger — reduces heat transfer and raises cabinet temperature.

How to fix Lennox furnace code E250: safe checks first

These are the only steps a homeowner should perform. Everything else lives inside the cabinet and is technician work.

• Replace the air filter. If it’s gray, matted, or you can’t see light through it, swap in a fresh one. Buy the size printed on the frame of the filter you pull out — don’t assume a standard size. This resolves a large share of E250 faults.
• Open supply registers and clear returns. Keep at least 80% of your supply registers fully open, and make sure furniture, rugs, or boxes aren’t blocking vents or return-air grilles.
• Check the thermostat. Confirm it’s set to Heat and the fan is on Auto (not permanently Off). Replace thermostat batteries if it’s a battery model.
• Cycle power once. Turn the furnace breaker (or the switch on the furnace) off for 30 seconds, then back on to allow one reset attempt. Do not repeatedly reset a unit that keeps faulting.
• Look for obvious duct problems you can see without tools — a disconnected flex duct or a fully closed damper handle.

If the code returns after a fresh filter and open vents, stop and call a technician. Repeated overheating can damage the heat exchanger.

How a technician will diagnose it

A qualified tech will typically:

• Measure temperature rise across the furnace and compare it to the rating-plate range — a high rise confirms low airflow.
• Check static pressure to pinpoint whether the restriction is the filter, coil, ductwork, or blower.
• Inspect and clean the blower wheel and verify the blower motor is running at the correct speed and drawing normal amps.
• Test the limit switch for continuity across its temperature range to confirm whether it’s tripping correctly or has failed open.
• Inspect wiring and connectors at the limit for breaks, corrosion, or loose terminals.
• Examine the heat exchanger and coil for blockage or buildup that traps heat.

A good quote should identify what caused the overheat — not just replace the limit switch and call it done.

Symptom, cause and what to do

Lennox furnace code E250 repair cost

Costs vary by region, model, and access. The cheapest and most common fix is a filter change, which is why it’s worth ruling out before scheduling a service call.

Related codes

We’re not listing sibling Lennox code numbers here. Lennox alert numbering differs between legacy two-digit LED SureLight boards, alphanumeric SureLight unit controllers, and iComfort-communicating systems, and a number that means one thing on one board series can mean something else on another. Publishing a guessed meaning for a pressure-switch or flame-sense code would send you down the wrong diagnostic path.

Instead, look up any other code your furnace is showing in the diagnostic legend printed inside the blower-compartment door, or in the service literature for your exact model number. If a second code appears alongside the limit fault and you can’t confirm what it means from your own documentation, treat it as technician work — especially anything involving the gas valve, pressure switches, venting, or flame sensing.