Lennox Furnace Reset: Clear Lockout Codes

Quick Answer

Most Lennox furnaces can be reset by flipping the power switch off for thirty seconds and then back on. If the unit is in a hard lockout due to a tripped rollout switch, you must manually press the small button between the wire terminals on the switch itself.

Nine times out of ten, a furnace stops running because the control board detected a minor fault and entered a safety lockout. Resetting the system clears these soft errors and forces the inducer motor to start its pre-purge cycle again. While a simple power cycle works for most ignition failures, recurring lockouts usually point to a dirty flame sensor or a clogged condensate line that needs professional attention.

LennoxFurnace

How to Reset Your Lennox Furnace

Resetting your Lennox unit is the first step I take on every service call to see if the error is persistent or a fluke. It reboots the integrated furnace control board and allows the internal logic to re-evaluate all safety sensors from a clean state. If the furnace fires up and then dies again, the reset has done its job by revealing the true underlying fault.

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Soft Lockout (Ignition Failure)55%

Limit or Rollout Trip25%

Power Surge or Board Glitch20%

Symptoms You May Notice

The furnace fires up briefly, you hear the ignitor click and a small whomp of the burners, and then everything shuts down completely within ten seconds. That's classic flame sensor failure right there.
LED status light on the control board is flashing a specific blink pattern, like three flashes, a pause, then three more. Write that down before you touch anything.
Blower fan is running continuously but only cold air comes out of the vents, not a hint of heat.
Thermostat says 'Heat On' and the room temperature just keeps dropping anyway.
You can hear the inducer motor spin up fine but the burners never actually light.

Tools Required for Diagnosis

Phillips #2 screwdriver (for cabinet door screws if panels are screwed down)Flathead screwdriverMultimeter (to test flame sensor resistance if furnace keeps relocking)Fine steel wool or 220-grit sandpaper (to clean the flame sensor rod)Flashlight or headlamp

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

Frequently Asked Questions

Where is the reset button on a Lennox furnace?

Most Lennox furnaces don't have a single button labeled Reset like your garbage disposal does. You reset them two ways. First is cycling the main power switch, that light-switch-looking thing on the side of the cabinet or a nearby wall. That clears the control board memory entirely. Second is the manual rollout switch near the burner assembly, a small disc about the size of a quarter with a center button that pops out when it trips. Press it back down until you feel a click. Those are your two reset points on basically every Lennox residential furnace made in the last fifteen years.

How many times can I reset my Lennox furnace?

Two strikes, then stop and call someone. Reset it once, it runs fine for a full day, probably just a fluke like a power blip or a temporary pressure hiccup. But if it trips again within twenty-four hours, something is actually broken. I've seen people reset their furnace six or seven times trying to muscle through a cold night, and they end up cracking the heat exchanger from all the thermal cycling stress. That turns a $150 flame sensor job into a $1,500 to $2,500 heat exchanger replacement or a full unit swap. Don't do that to yourself.

Why does my Lennox furnace keep going into lockout?

Nine times out of ten when I get a callback on a furnace that won't stay running, it's the flame sensor. That little rod gets coated in white oxidation and the control board can't confirm combustion is happening, so it cuts the gas as a precaution even though the flame is actually burning fine. Second most common thing I find is a dirty filter. If yours is gray and packed solid, you're choking the heat exchanger and tripping the high-limit. Third, especially on high-efficiency models, is a blocked condensate drain line. Check those three things in that order before you do anything else.

Will resetting the furnace fix an LED error code?

It'll clear the code temporarily, sure. But the Lennox control board will flash the same code again within a few minutes if the underlying problem is still there. Here's what you should do before you flip that power switch: count the blink pattern on the LED and write it down or take a quick video with your phone. That blink sequence tells you exactly what the board detected. Three blinks means one thing, five blinks means something completely different. You can look it up in your furnace manual or search 'Lennox [blink count] blinks meaning.' Don't lose that diagnostic info before you record it.

Do I need to reset the furnace after changing the air filter?

Not usually. If the furnace locked out because of a restricted filter, swapping in a clean one and doing a normal power cycle reset is enough to get it running again. But here's something a lot of people don't realize: if you grabbed a MERV 13 or higher filter at the hardware store because you thought higher is better, those thick filters can restrict airflow almost as badly as a dirty cheap one. Most Lennox residential furnaces are designed for MERV 8 to 11. Check your manual for the recommended rating before you buy the next one.

Models Known to Experience RESET-PROCEDURE Errors

This repair applies to most Lennox furnaces with this error code. Common model numbers include:

EL296VH110XE60C, SLP98UH090XV48C, ML193UH090XP48C, EL195UH090XE48C, SL280UH090V48C, ML195UH070XP36B, EL180UH090E60D, SLP98V090U48B

Written by

Raj Patel

HVAC & Water Systems Specialist · 15 years experience

Last verified for technical accuracy on March 17, 2026