Trane Furnace Light Blinking? What the Flashes Mean

First, breathe: on Trane furnaces, some blinking is good news. A slow, steady blink on many models just means the board is powered and idle, and a faster blink often means it's actively heating. The trouble codes are the counted bursts — flash-flash-flash, pause, repeat.

Safety first, every page: smell gas, leave the house, call your gas company from outside. That outranks every code on this page.

How to read it

Watch the light through the small window in the lower front panel. If it blinks a number of times, pauses, and repeats the same number, that count is the code. Before you reset anything:

• Write down the count and the model number (sticker inside the upper panel). Power-cycling wipes the code.
• Your furnace's own legend is printed inside the door panel — it beats any website's list, including this one. The codes below are common across many Trane and American Standard models.

Common Trane flash codes

• Slow steady blink — normal standby. Not a fault.
• Fast steady blink — normal call for heat on many models.
• 2 flashes — external lockout: the furnace failed at something (usually ignition) enough times to give up. Often clears with a power cycle, then returns until the cause (commonly a dirty flame sensor) is fixed.
• 3 flashes — pressure switch fault: it can't prove the vent is drawing. Check the outside vent pipes for snow, ice, leaves, or nests. That fix is free and takes one minute.
• 4 flashes — high temperature limit: it overheated. The usual suspect is a clogged filter or blocked vents. Filter to the light; can't see through it, replace it.
• 5 flashes — flame sensed when there shouldn't be flame. Turn it off and call a pro.
• 6–9 flashes — polarity, grounding, or blower issues. Pro territory.

The one-reset rule

After fixing the obvious (filter, vents, outdoor pipes), reset once: power switch off 30 seconds, back on. If the same code comes back, stop. Repeated resets against a real fault do real damage — and you already have the two things the repair call needs: the code and the model number.

American Standard owners

American Standard and Trane are the same family; most models blink the same codes the same way.

Related symptoms

• Furnace won't turn on
• Furnace clicks but won't ignite
• Furnace shuts off after a few seconds

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