Trane code 1 flash

What this code means

One flash on the status LED indicates the furnace is in lockout after ignition failure — the control attempted the ignition sequence the maximum number of times without proving flame.

Which models show it

Trane XV80, XV90, S9X1, S9V2, XC80, and XC95 gas furnaces with the standard diagnostic LED behind the lower door viewport.

What is actually happening

The furnace tries to light, fails flame proving, waits, and retries until it enters hard lockout shown as one flash. No heat until lockout is cleared and the fault is addressed.

Is it safe to keep running?

Do not bypass lockout. Wait at least one hour or power cycle once after checking gas and filter — then call for service if lockout returns.

What a homeowner can safely check

• Confirm gas supply and that the shutoff at the furnace is on.
• Install a clean filter — severe restriction can contribute to ignition failures on marginal systems.
• Check the viewport LED pattern after a failed cycle — count flashes only when the call for heat is active.
• Ensure the lower door is fully latched so interlocks engage.

When to stop

• Lockout returns after a single power cycle.
• You smell unburned gas during ignition attempts.
• Flames are yellow or lazy when ignition briefly occurs.

Likely causes ranked

1. 1. Dirty flame sensor

   How a tech confirms: Microamp reading on flame rod during test fire; cleans or replaces sensor.

   Typical repair: $150–$325 · Air Conditioner Repair cost guide

2. 2. Failed igniter

   How a tech confirms: Resistance check on HSI; observes ignition sequence with gas valve metered.

   Typical repair: $200–$475 · Furnace Replacement cost guide

3. 3. Gas valve or gas pressure issue

   How a tech confirms: Inlet/outlet pressure test; verifies valve coil and wiring harness.

   Typical repair: $250–$600 · Air Conditioner Repair cost guide

4. 4. Control board ignition output failure

   How a tech confirms: Compares board outputs to Trane service chart; may update firmware on communicating models.

   Typical repair: $450–$950 · Furnace Replacement cost guide

Is this the end of this unit?

Board-plus-valve repairs on furnaces past 15 years often exceed half the cost of a new S9 series install — compare quotes using the furnace replacement guide.

How to clear the code

Turn off power at the furnace for 30 seconds or wait one hour for soft lockout timers. Restore power and set thermostat to heat 3°F above room temp.

Why clearing is not fixing it: Lockout clears after time or power cycle, but ignition failures repeat until flame proving components or gas delivery are repaired.

Which trade to call

Call a licensed hvac contractor who works on furnace equipment. Gas, refrigerant, and combustion faults are not general handyman jobs.

Related codes and symptom guides

Symptom guide: Furnace Not Heating

FAQ

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