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ErrBase

Lennox Furnace Error Code 270: Ignition Failure Lockout

Quick Answer

Lennox furnace error 270 is an ignition lockout after multiple failed attempts. The furnace tried to light the burners and failed each time. Start by cleaning the flame sensor rod with 0000 steel wool: the thin oxide coating on the sensor surface blocks the microamp signal the board uses to confirm flame.

Lennox furnace error 270 is an ignition lockout after multiple failed attempts. The furnace tried to light the burners and failed each time. Start by cleaning the flame sensor rod with 0000 steel wool: the thin oxide coating on the sensor surface blocks the microamp signal the board uses to confirm flame. If cleaning does not fix it, inspect the hot surface ignitor for cracks or dark spots and test its resistance (40-90 ohms cold for silicon nitride). Also confirm the gas shutoff valve is fully open. Flame sensor costs $10-20; ignitor costs $25-50 for Lennox models.

LennoxFurnaceSeverity: highDifficulty: intermediate80% DIY Success
Time to Fix
20–75 min
Difficulty
intermediate
Parts Cost
$10 – $50
Tools Needed
Multimeter (DC microamps and resistance modes), 0000 steel wool or fine emery cloth
Wrong code?

Not seeing 270 on your display?

Select what your appliance is actually doing and we'll take you to the right guide.

all lennox furnace error codes
HUB
inducer motor failure or stall
E228
fault code reset procedure
RESET

What Does the 270 Code Mean?

Ignition lockout after repeated failures. Clean the flame sensor first. If that does not resolve it, test and likely replace the hot surface ignitor.

Most Likely Causes

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

Hot surface ignitor cracked or thermally degraded40%
Flame sensor rod coated with oxide film24%
Gas valve not opening on command22%
Gas supply pressure low or manual shutoff partially closed14%

Symptoms You May Notice

  • Code 270 displayed on Lennox SL280V or EL296V control board
  • Furnace goes through startup sequence but produces no flame or flame extinguishes immediately
  • Ignitor glows but gas does not ignite, or gas ignites briefly then cuts out
  • Furnace was lighting occasionally before going into full lockout
  • Furnace restarts on reset but returns to 270 within one to three attempts

Can you reset a Lennox furnace to clear the 270 code?

After cleaning the flame sensor or replacing the ignitor, set the thermostat to OFF for 30 seconds then back to HEAT. Code 270 clears automatically after one successful full ignition cycle where the flame sensor confirms a stable flame. If code 270 returns, cycle the circuit breaker off for 30 seconds before the next attempt. Do not perform more than two resets without addressing the root cause.

Tools Required for Diagnosis

Multimeter (DC microamps and resistance modes)0000 steel wool or fine emery clothFlathead and Phillips screwdriversWork glovesFlashlight

Diagnostic Checklist

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

1

Turn off power at the circuit breaker and allow 5 minutes for cooling

Turn off power at the circuit breaker and allow 5 minutes for cooling. Open the lower cabinet access panel and locate the flame sensor: a single-wire thin metal rod extending at an angle into the burner flame path, held by one mounting screw. Remove the screw and disconnect the wire terminal. Examine the rod surface. A clean sensor is bright silver. A fouled sensor has a white, chalky, or grayish coating that must be removed.

2

To confirm the flame sensor is functioning after cleaning

3

With power off

4

Verify gas supply

5

If all parts test good

Replacement Parts

If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.

Part Name
Hot Surface IgnitorH0909082A · $25–$50
Flame Sensor10L61 · $10–$20

Repair vs. Replace Calculator

Appliance Age (Years)7 Yrs
Labor Approach
Our Verdict
REPAIR
Estimated Cost: $30 (Parts) vs $3400 (New Machine)

Frequently Asked Questions

How do I clean the flame sensor on a Lennox SL280V or EL296V furnace?
Turn off power at the circuit breaker and wait 5 minutes for components to cool. Open the lower cabinet door. The flame sensor is a thin metal rod extending into the burner flame path, secured by a single screw. Remove the screw, disconnect the push-on wire terminal, and pull the sensor out. Use 0000-grade steel wool or fine emery cloth to gently polish the metal rod until the surface is bright and shiny. Do not use coarse sandpaper. Wipe the rod clean with a dry cloth, reinstall, reconnect the wire, and test.
What causes Lennox furnace code 270 to keep coming back?
If code 270 returns after cleaning the flame sensor and replacing the ignitor, the next most likely causes are: low gas pressure from the utility (most common in peak winter demand), a gas valve that is slow to open or not opening fully, or a control board timing issue where the flame proving window is too short. A technician can use a combustion analyzer and gas pressure gauge to identify which of these is occurring.
Can I test a Lennox furnace flame sensor without a multimeter?
You can perform a basic functional test by cleaning the sensor, resetting the furnace, and observing whether the burners stay lit after the ignitor shuts off. If the flame lights and stays on for more than 10 seconds but then cuts out, the sensor is producing a marginal microamp signal that is dropping below the control board's minimum threshold. This confirms a sensor problem even without a microamp reading. However, a multimeter test gives you the exact signal strength and removes guesswork.
What is the ignitor part number for a Lennox SL280V furnace?
The common hot surface ignitor part number for the Lennox SL280V is H0909082A. However, verify by your specific model's BTU rating and revision level using the Lennox parts lookup at lennox.com or at an authorized Lennox parts distributor. Some SL280V variants use a different bracket configuration. The ignitor is a standard silicon nitride type shared across many Lennox models and available from most HVAC supply houses.
Is Lennox code 270 the same as other brand ignition lockout codes?
Functionally yes: code 270 on Lennox is equivalent to Code 14 on Carrier, Code E12 on Trane, and similar ignition lockout codes on other gas furnace brands. All represent the same event: the control board made multiple ignition attempts without confirming a flame and locked out for safety. The root causes (dirty flame sensor, failed ignitor, gas supply issue) are also similar across all brands.

Related Lennox Furnace Error Codes

Code: HUBLennox Furnace Error Codes: Complete SL280V and EL296V Fault ReferenceCode: E228Lennox Furnace E228 Error Code: Inducer Motor FaultCode: RESETHow to Reset a Lennox Furnace

Models Known to Experience 270 Errors

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

SL280V, EL296V, XC21, SL297NV, EL180UH

Last verified for technical accuracy on March 14, 2026