Carrier 59SC2B Error Code Continuous OFF: No Power / Control Failure

What Does Code Continuous OFF Mean?

A continuously off LED on the Carrier 59SC2B is not a blink code at all — it is the absence of any indication, and it tells you the HK42FZ034-type furnace control board is receiving no power. Because this board manages every stage of operation (inducer, hot surface igniter, gas valve, and blower), the furnace is completely dead until power is restored.

The most common reason is a tripped circuit breaker or a blown fuse at the electrical panel. The next most likely cause is the furnace's own power switch — on the 59SC2B this is usually a standard toggle switch mounted on or beside the cabinet that is easily mistaken for a room light switch and bumped off. Both of these are homeowner-checkable.

If the breaker and switch are both fine, the fault lies deeper. Carrier's service label instructs a technician to verify 115 VAC at L1 and L2 and 24 VAC at SEC-1 and SEC-2. A missing 24 VAC reading with 115 VAC present points to the transformer or a blown secondary fuse (see code 24), while a dead board with good voltage feeding it means the control itself has failed. Those voltage checks require a meter and are not DIY.

What You'll Notice

• The control board status light is completely dark — no steady glow and no flashing
• The furnace does not respond to the thermostat at all: no inducer, no igniter, and no blower
• The thermostat screen may be blank if it is powered from the furnace's 24V (C) connection
• Other 115V loads sharing the furnace breaker may also be dead

Common Causes

How This Is Diagnosed

Diagnosis works from the panel inward. The breaker and furnace disconnect switch are confirmed on first, then the blower-door interlock switch (which cuts all power when the panel is loose) is checked for proper seating. Only after those pass does a technician measure 115 VAC at L1/L2 and 24 VAC at SEC-1/SEC-2 to decide between an incoming-power problem, a failed transformer, or a dead control board.

How to Fix It: Check the Circuit Breaker, Power Switch, and Blower Door

What You'll Need

• Flashlight
• Replacement fuse of the same amperage (if your panel uses fuses)

Steps

1. Turn off power at the breaker and shut off the gas supply as a precaution Before investigating, switch the furnace breaker to OFF and turn the manual gas shutoff valve near the furnace to the OFF position (handle perpendicular to the pipe). If you smell gas at any point, leave immediately and call your gas company.
2. Reset the circuit breaker At the main electrical panel, find the breaker for the furnace or HVAC circuit. If it sits in the middle (tripped) position, flip it fully to OFF, then back to ON. If your panel uses fuses, check the furnace fuse and replace a blown one with the same amperage.
3. Check the furnace power switch Look for a standard toggle switch on or beside the furnace cabinet (sometimes at the top of the basement stairs). Confirm it is ON. This switch looks like an ordinary light switch and is a very common accidental cause of a dead 59SC2B.
4. Confirm the blower door is fully seated The 59SC2B has a door interlock switch that cuts all power when the blower-compartment panel is loose or removed. Make sure the panel is pushed in squarely and latched so the interlock plunger is depressed.
5. Restore gas and power, then test Turn the gas valve back to ON (handle parallel to the pipe) and switch the breaker and power switch to ON. Through the control-board sight glass the LED should now be continuously on (normal standby). Set the thermostat to call for heat and confirm the furnace starts.

When to Call a Professional

Contact a licensed HVAC technician if:

• The breaker trips again immediately each time it is reset
• The breaker and power switch are both on, but the LED stays completely dark
• There is a burning smell, scorching, or visible damage near the furnace or its wiring
• You are not comfortable working at or around the electrical panel

✓ Verified against manufacturer service manual — March 2026