Home Fault Codes

Carrier Furnace Error Code 12: Meaning and Fix

Applies to: Carrier 58STA and 58STX single-stage induced-combustion furnaces with a two-digit status code LED.

12
How 12 appears on a Carrier furnace display.

Also shown as: 1 short 2 long, 1 short, 2 long flashes

Reading the furnace display

A furnace reports faults on a small status LED on the control board, seen through the sight glass in the blower door, or on a two-digit display. Watch a full cycle of the pattern and count the flashes, including the pause between groups, before you decide what you saw. The code chart is on the label inside the blower door.

This page lists the fault codes this brand documents, with likely causes and a short repair path. The codes apply to model numbers such as 58STA and 58STX; check the label on your unit to confirm yours.

What causes 12

How to fix it

If you smell gas, leave the building and call your gas utility from outside; do not touch switches or the furnace. Switch the furnace power off before you open the blower door or touch the igniter or flame sensor, and call a licensed HVAC technician if you are not sure.

The code meaning comes from the manufacturer document listed under Sources. The causes and steps below are general troubleshooting guidance, not the manufacturer's service procedure.

  1. Wait about 90 seconds. The blower stops by itself and normal operation follows.
  2. If the code appears again and again, look for a loose power connection, a failing breaker, or a power switch being flipped.
  3. Check the thermostat wiring at the furnace and at the thermostat for loose connections.
  4. If it repeats after those checks, have a technician check the 24 volt circuit and the control.
  5. Restore power and run a heating cycle. If the code returns, call a licensed HVAC technician and give them the code, the board label and the furnace model number.

Questions

What does 12 mean on a Carrier furnace?

Code 12 (1 short, 2 long flashes) on a Carrier furnace means the blower is running for 90 seconds after power was applied during a call for heat, or after the thermostat call ended during the blower on-delay. It is a status message.

Can I reset the furnace myself?

The control can be reset by switching power off at the furnace switch or breaker for about 30 seconds, which clears some lockouts. If the same code returns, the fault is still present and the control will shut the furnace down again. Never bypass a safety switch to keep it running.

When should I call a technician?

Call a licensed HVAC technician for anything involving gas, the pressure switch, the limit or rollout switches, the igniter, the flame sensor or a control board replacement, or if the code keeps coming back after the simple checks.

Other brands with code 12

The same code can mean something different on another maker's appliance. Check the brand before you act.

Bryant furnaceBlower on after power upChamberlain garage door openerSafety sensor wire shorted or reversedCraftsman garage door openerSafety sensor wire shorted or reversedLiftMaster garage door openerSafety sensor wire shorted or reversedNoritz tankless water heaterFlame lossPayne furnaceBlower on after power upRheem tankless water heaterGas service interrupted or LP gas lowRinnai tankless water heaterFlame failure

Other Carrier furnace codes

Continuous OffNo power to the control board (LED stays dark)Continuous OnNormal: control board has 24 volt power (LED steady on)Rapid FlashingLine voltage polarity reversed (LED flashing rapidly)11No previous fault code stored13Limit circuit lockout14Ignition lockout

Sources

Part numbers are OEM references; confirm fit by your model number before ordering. Meanings compiled from manufacturer and parts-retailer documentation; see sources below. Unplug the appliance before opening it.

Applies to models including 58STA, 58STX.