Trane Furnace Error Codes: What Each Blink Means

Trane furnace error codes come from the integrated furnace control (IFC), the circuit board inside the lower blower compartment. You usually see the LED through a small sight window in the door. This guide lists the Trane furnace error codes confirmed in Trane’s own service installer’s guides, grouped by control board family, so you can work out what your furnace is telling you.

Trane and American Standard furnaces are built by the same company (Trane Technologies), and Trane’s service guides list model numbers as “A” or “T” at the start. That means the codes here apply to both brands. HomeCodeFix is independent and not affiliated with either brand.

Why do Trane furnace blink codes differ from model to model?

Trane has used several different control boards over the years, and each board family has its own flash code chart. For example, 2 flashes means “system lockout” on many single-stage boards but “pressure switch stuck closed” on some two-stage boards. Trane’s own troubleshooting page says what the lights mean depends on the furnace’s make and model.

The chart that matches your furnace is printed on a label (Trane calls it a mnemonic label) or on the wiring diagram attached to the blower door. When a board is replaced, Trane’s kit instructions tell the installer to stick a new label on the door, so the door chart should match the board inside. Always trust the chart on your own door over any list online, including this one.

To find your board family:

1. Look at the rating plate inside the furnace cabinet for the full model number.
2. Note the first letters (for example TUD2, TDX, AUX). The letter after the brand letter and the “2” or “R” help identify the family.
3. Compare the chart on your door with the tables below.

Trane furnace error codes list

This master table shows the confirmed meanings for the most common blink counts. Where a count means different things on different boards, both meanings are listed. “Standard boards” means the single-stage and two-stage variable boards covered in Trane guides 18-CH49D1, 18-CH92D1 and 18-CH111D1. “Two-stage W-R boards” means the two-stage boards covered in guides 18-CH61D1 and X341956P04.

For other brands, see our Lennox furnace error codes guide or browse every furnace error code guide.

What do the codes mean on standard single-stage Trane boards?

On the standard Trane single-stage silicon nitride (SiNi) control, the red LED counts from 2 to 9 flashes, and slow or fast flashing means everything is normal. This is the chart Trane prints in its service guide 18-CH49D1-1 for the SiNi integrated furnace control. Trane’s single-stage replacement control guide 18-CH92D1-1A-EN shows the same meanings.

Trane’s two-stage variable-speed replacement control (guide 18-CH111D1-1A-EN, for models starting TUX, TDX, AUX and ADX) uses the same 2 to 9 list. On that board, 4 is “open limit switch,” 6 is “115 volt AC power reversed or improper ground” and 9 is “igniter relay fault.” It also lists 1 flash about every 20 seconds as normal operation.

What do the codes mean on Trane two-stage boards?

Many two-stage Trane and American Standard furnaces use a board with a red fault LED, an amber status LED and a green LED, and the red codes start at 1 flash. Trane’s guides 18-CH61D1-4A-EN (models starting *UD2, *DD2, *UD and *DD) and X341956P04 (models such as *UD080R9V3) show this layout. If your door chart lists amber and red columns, use this table.

Red LED (fault) codes

Amber LED (status) codes

The amber patterns 3 and 4 usually point to thermostat wiring or settings, not a furnace failure. Rapid amber flashing is an early warning that the flame sensor signal is weak, which is often a dirty flame sensor.

What do the codes mean on Trane communicating furnaces?

Trane communicating furnaces (model numbers with “ACV,” such as *UD2B080ACV32A) use a chart close to the standard one, plus two extra codes. Trane guide 18-CH76D1-1A-EN lists these meanings:

• 1 flash every 20 seconds: normal operation
• 2: system lockout, retries or recycles exceeded
• 3: pressure switch fault
• 4: open limit switch
• 5: flame sensed when no flame should be present
• 6: 115 V AC power reversed (polarity) problem
• 7: gas valve circuit error
• 8: low flame sense signal
• 9: open inducer limit
• 10: communication fault
• Continuous on or off: internal control failure or fuse open

On communicating systems, the thermostat or control may also show an alert. A communication fault (10) often means a wiring problem between the furnace and the communicating thermostat or outdoor unit.

What do the codes mean, grouped by system?

Most Trane furnace error codes fall into five groups: ignition and flame, venting and pressure switch, overheating and limits, power and wiring, and the control board itself. Knowing the group helps you decide whether a safe check might help or whether you need a technician right away.

Ignition and flame codes

These include system lockout (2 on standard boards; 7 and 8 on two-stage boards), low flame sense (8 on standard boards; rapid amber on two-stage boards), and igniter faults (9 on standard boards; 12 on two-stage boards).

• Lockout means the furnace tried to light several times and failed, or the flame kept dropping out. Common causes are a closed gas valve, a dirty flame sensor or a failing igniter.
• Low flame sense means the flame is lit but the board can barely detect it. A technician can usually clean the flame sensor.
• Igniter fault means the board sees a problem in the igniter circuit. The igniter is fragile and very hot, so leave it to a pro.

Other brands use similar logic. See our guides to Carrier furnace code 13 flame lockout and Carrier furnace code 34 ignition failure for comparison.

Venting and pressure switch codes

These include 3 flashes on standard boards and 2, 3, 3 double and 6 flashes on two-stage boards. Trane’s own chart for code 3 lists three possible problems: venting, the pressure switch and the inducer.

• The pressure switch proves that the inducer fan is pulling exhaust out through the vent. If it does not close, the furnace will not light.
• A blocked outdoor intake or exhaust pipe (snow, ice, leaves, nests) is a common cause on high-efficiency furnaces.
• On condensing furnaces, water trapped in the pressure switch hose or a clogged condensate drain can also trip it.

“Stuck closed” (2 flashes on two-stage boards) is different: the switch says there is draft when the inducer is not running, which usually points to a failed switch or wiring. For a similar fault on another brand, read Goodman furnace 3 flashes and Carrier furnace code 31.

Overheating and limit codes

These include 4 flashes on most boards, 5 flashes on two-stage boards (rollout), 11 flashes (limit open, blower failure) and 9 on communicating boards (open inducer limit).

• The high limit switch opens when the heat exchanger gets too hot. The most common cause is restricted airflow: a dirty filter, closed registers or a blocked return grille.
• The rollout switch opens when flame rolls out of the burner area. That can mean a blocked flue or heat exchanger problem, so it always needs a technician.
• A blower failure stops air from carrying heat away, which then trips the limit.

Power and wiring codes

These include 6 flashes on standard boards and 9 flashes on two-stage boards. Trane’s guides note that the control is polarity sensitive: the hot leg of the 115 V power must connect to the black field lead. Poor grounding or low voltage can also trigger the code.

Steady off with no light at all usually means no power reaches the board. Check the furnace power switch, the breaker and that the blower door is fully closed. Trane notes that some furnaces have a door switch that cuts power when the door is off.

Gas valve and control board codes

These include 7 flashes on standard boards, 10 flashes on two-stage boards, and a steady on light. A gas valve circuit error or gas flow with no call for heat are serious faults. Trane’s charts say a continuous on light, or a solid red on two-stage boards, means the control should be replaced.

If the code says gas is flowing when it should not be (10 on two-stage boards) or flame is sensed with no call for heat, shut off the gas to the furnace and call a technician.

How do you read the blink code on a Trane furnace?

Look through the small window in the lower (blower) door, count the red flashes between the longer pauses, and write the number down before you touch anything. Trane’s troubleshooting page says to note the lights, the blink pattern or the error code first. Cutting power can clear the code, so record it before any reset.

Trane also warns against removing the front panel while the furnace is running. If you cannot see the LED without opening the door, note that opening the door may cut power and clear the code.

What can you safely check yourself?

You can safely check the thermostat, the filter, the power switch and breaker, the gas valve handle position and the outdoor vent pipes. Trane’s support page tells homeowners not to try to repair the furnace themselves because of electrical and gas hazards, and doing so may void the warranty. Anything inside the burner compartment belongs to a licensed technician.

• Thermostat: set to Heat and at least a few degrees above room temperature. Replace thermostat batteries if the display is blank.
• Filter: Trane recommends changing standard filters every 30 to 90 days. A clogged filter is the top cause of limit codes.
• Registers and returns: open supply vents and clear furniture off return grilles.
• Power: the furnace switch (often looks like a light switch near the unit) is on, and the breaker is not tripped.
• Vents outside: on high-efficiency furnaces, clear snow, ice or debris from the white plastic intake and exhaust pipes.
• Gas: make sure other gas appliances work and the furnace’s manual gas shutoff handle is in line with the pipe (open).

How do you reset a Trane furnace?

To reset a Trane furnace, turn the thermostat off, switch off power to the furnace for about 30 seconds, restore power, then call for heat and watch the start-up sequence. Some lockouts clear on their own after a waiting period; Trane’s two-stage chart lists a 1-hour lockout for repeated pressure switch openings. Only reset once or twice. If the same code comes back, the furnace is protecting you from a real fault.

What should you do for safety when a Trane furnace shows a code?

When should you call a pro for Trane furnace error codes?

Call a licensed HVAC technician when a code returns after one reset, or when it involves the flame, gas valve, rollout, wiring or the control board. Trane’s own advice is to call for repair and tell the scheduler the code you saw plus your brand and model. Most fixes behind the burner door need gas and electrical training.

Call a pro right away if:

• The code points to flame sensed with no call for heat, gas flow with no call for heat, or rollout.
• You see 2 or 3 flashes again after clearing vents and changing the filter.
• The LED is steady on, or a code says to replace the IFC.
• You hear booming at ignition, see soot, or smell exhaust.
• Your CO alarm has gone off at any time.
• Power or polarity codes appear (6 on standard boards, 9 on two-stage boards).

The U.S. Consumer Product Safety Commission (CPSC) urges a yearly professional inspection of furnaces, including the flues and vents, to help prevent carbon monoxide problems. That visit is also a good time to have the flame sensor cleaned.

How can you prevent Trane furnace error codes?

Most nuisance codes come from airflow and venting problems, so a clean filter, clear vents and yearly service prevent many of them. These habits cost little and protect the heat exchanger.

• Change the filter every 30 to 90 days, as Trane suggests, and more often with pets.
• Keep supply registers open and return grilles clear.
• After snow or storms, check that outdoor intake and exhaust pipes are clear.
• Schedule a yearly furnace tune-up before the heating season, as Trane and the CPSC recommend.
• Have the condensate drain on high-efficiency models checked during service.
• Test CO alarms monthly and replace batteries as the alarm maker directs.

Frequently asked questions

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