Carrier · Status code
Carrier 59SC6A status code 12.1: W on at power up
Status code 12.1 means the control saw a thermostat heating demand (W input) present at the moment power was restored to the furnace. The control runs a 90-second blower-only recovery period, shows 12.1 during it, then responds to the thermostat normally.
On the control
- Code
- 12
- Minor
- 12.1
- Door LED
- 1 short flashes then 2 long
- Controller
- 59SC6A integrated furnace control with 3-digit LCD display and door LED
- Applies to
- Carrier Comfort 96 (59SC6A)
- Manual
- 59SC6A-01SI REV D
What each minor code says, verbatim
| Display | Manufacturer wording |
|---|---|
| 12.1 | W on at power up |
A code is a condition, not a diagnosis
Code 12.1 is informational and self-clears after the 90-second delay unless a thermostat wire fault keeps the W input stuck on. If it repeats without a power event, the thermostat circuit should be checked for a stuck call.
Which furnaces this applies to
Documented for Carrier 59SC6A Comfort 96 furnaces in installation instructions 59SC6A-01SI REV D. It appears after power returns while the thermostat is still calling and is a normal recovery behaviour.
Scope: Carrier 59SC6A Comfort 96 furnaces with the on-board 3-digit display control. Not sure which control you have? Send us the full model number from the rating plate.
Safe things to look at first
- Read the full code on the control display through the door, including any minor digit (for example 33.2), and write it down.
- Look, without touching, for obvious conditions you can report: snow or ice at the vent terminations, water on the floor, a loaded filter, a condensate pump that is full or off.
- Note whether the furnace still heats at all, and how long it runs before the code returns.
- Wait one to two minutes after a power interruption; code 12.1 clears on its own when the delay finishes.
Do not
- Do not bypass or jumper the door switch, limit switches, rollout switches or pressure switches.
- Do not open the burner compartment, disconnect tubing, or adjust the gas valve or gas pressure.
- Do not keep cycling power to force the furnace to relight; repeated resets hide the fault and can allow unburned gas to build up after ignition failures. If the code returns, stop and call.
What a technician does
- A technician confirms the 24 V thermostat wiring and the thermostat's heating-call behaviour if 12.1 repeats without a power event.
Related components and symptoms
Questions people ask
My furnace shows 12.1 after a power outage. Is something wrong?
Not by itself. The code is shown during the control's 90-second blower-only recovery after power returns while the thermostat is calling. It should clear on its own.
Seeing code 12 on your Carrier?
Tell us the full code, the model number and whether the furnace still heats on low. BC Wide prioritizes no-heat calls across Greater Vancouver.