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ErrBase

Trane Furnace E12 Error Code: Ignition Lockout

Quick Answer

Trane furnace E12 is a full ignition lockout after three failed ignition attempts. The furnace went through the full startup sequence (inducer on, ignitor glowing, gas valve opening) at least three times without detecting a confirmed flame, then locked out. Start by cleaning the flame sensor rod with 0000 steel wool, as sensor fouling is the most common cause.

Trane furnace E12 is a full ignition lockout after three failed ignition attempts. The furnace went through the full startup sequence (inducer on, ignitor glowing, gas valve opening) at least three times without detecting a confirmed flame, then locked out. Start by cleaning the flame sensor rod with 0000 steel wool, as sensor fouling is the most common cause. If cleaning does not resolve it, test the hot surface ignitor for visible cracking and measure its resistance (40-90 ohms cold for a silicon nitride ignitor). Also verify the gas supply shutoff valve is fully open.

TraneFurnaceSeverity: highDifficulty: intermediate79% DIY Success
Time to Fix
25–75 min
Difficulty
intermediate
Parts Cost
$10 – $50
Tools Needed
Multimeter (microamp DC and resistance modes), 0000 steel wool
Wrong code?

Not seeing E12 on your display?

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

all trane furnace error codes
HUB
rollout limit tripped
E2.1
fault code reset procedure
RESET

What Does the E12 Code Mean?

Furnace locked out after three ignition failures. Clean the flame sensor first. If that does not fix it, check the hot surface ignitor and gas supply.

Most Likely Causes

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

Flame sensor rod coated with oxide film blocking microamp signal40%
Hot surface ignitor cracked or failed to reach ignition temperature24%
Gas valve not opening at correct time or not fully opening22%
Gas supply pressure low or manual shutoff valve partially closed14%

Symptoms You May Notice

  • E12 displayed on the furnace control board digital display
  • Furnace completely unresponsive after multiple startup attempts
  • Ignitor visibly glows during startup but no sustained flame
  • Furnace ran for a few cycles earlier then stopped lighting
  • No clicking from gas valve or gas valve clicks but no ignition

Can you reset a Trane furnace to clear the E12 code?

After cleaning the flame sensor or replacing the ignitor, set the thermostat to OFF for 30 seconds then back to HEAT. The E12 code clears automatically after one successful full ignition cycle. If E12 returns on the next attempt, flip the circuit breaker off for 30 seconds before retrying. Do not reset more than twice before investigating further.

Tools Required for Diagnosis

Multimeter (microamp DC and resistance modes)0000 steel woolFlathead and Phillips screwdriversWork gloves

Diagnostic Checklist

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

1

Turn off the circuit breaker and wait 5 minutes for internal

Turn off the circuit breaker and wait 5 minutes for internal components to cool. Open the lower cabinet and locate the flame sensor: a single-wire thin metal rod angled into the burner flame path, secured by one screw. Remove the screw and pull the sensor out. Disconnect the wire terminal. Inspect the rod surface: it should be bright silver metal. A white or grayish coating means it needs cleaning.

2

After cleaning, reinstall the flame sensor and reconnect the wire

3

With power off, locate the hot surface ignitor

4

Verify the manual gas shutoff valve behind or beside the furnace

5

If flame sensor and ignitor both test good and gas supply is

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 IgnitorSEN00107 · $25–$50
Flame SensorSEN00885 · $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 many times does a Trane furnace try to ignite before showing E12?
Most Trane furnaces attempt ignition three times before triggering the E12 lockout. The board waits a brief period between each attempt. After the third failed attempt, it stores the E12 code and locks out until manually reset via the thermostat or circuit breaker.
Why does my Trane furnace sometimes light and other times show E12?
An intermittent ignition failure that sometimes works and sometimes fails is characteristic of a marginally coated flame sensor or a hot surface ignitor that is thermally degrading. On cold starts, a borderline ignitor may not reach full temperature every time. Clean the flame sensor first. If intermittent failure persists, replace the ignitor even if it has not completely failed, as preventive replacement is far cheaper than an emergency service call in January.
Can I reset a Trane E12 lockout without calling a technician?
Yes. The E12 reset is a standard homeowner-level procedure: set the thermostat to OFF for 30 seconds then back to HEAT, or flip the circuit breaker off for 30 seconds. Cleaning the flame sensor before resetting is also a homeowner task requiring only a screwdriver and fine steel wool. Ignitor replacement is somewhat more involved but does not require special tools or licenses. Call a technician if E12 persists after both sensor cleaning and ignitor replacement.
What resistance should a Trane furnace hot surface ignitor read?
A silicon nitride hot surface ignitor on a Trane furnace should measure 40-90 ohms resistance at room temperature when tested with a multimeter set to resistance mode. Silicon carbide ignitors on older Trane models (pre-2010) may read 40-100 ohms. An OL reading means the ignitor is open-circuit and has failed. A reading below 20 ohms may indicate an internal short.
After cleaning the flame sensor, how do I know if Trane E12 is resolved?
Reset the furnace after cleaning the sensor and watch it complete one full startup sequence: inducer on, pre-heat period, ignitor glowing, gas valve click, flame lights, and blower starts shortly after. If the furnace completes that sequence and runs for 10-15 minutes without fault, the E12 is resolved. Monitor the next 3-4 heat cycles to confirm the repair is stable.

Related Trane Furnace Error Codes

Code: HUBTrane Furnace Error Codes: Complete Fault GuideCode: E2.1Trane Furnace E2.1 Error Code: Rollout Switch OpenCode: RESETHow to Reset a Trane Furnace

Models Known to Experience E12 Errors

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

XC95m, XV95, S9X2, XR95, XB80

Last verified for technical accuracy on March 14, 2026