Carrier 59SC2B Error Code LED Off (Continuous Off): No Power / Control Failure

What Does Code LED Off (Continuous Off) Mean?

When the amber LED on your Carrier 59SC2B control board stays completely off, it means the board is receiving no electrical power at all. The board needs both 115VAC line voltage (at the L1 and L2 terminals) and 24VAC secondary voltage (at SEC-1 and SEC-2) to operate. Without power, the furnace cannot respond to thermostat calls or run any heating cycle.

This is one of the most common furnace "errors" and, fortunately, one of the easiest to resolve. In most cases, the issue is upstream of the furnace itself — a tripped circuit breaker, a turned-off power switch on or near the furnace, or a door panel that isn't fully seated (which disengages the door safety switch).

If the breaker, power switch, and door panel all check out, the problem may be a failed transformer or a blown 3-amp fuse on the control board. These components require a technician to diagnose and replace safely.

Common Causes

How to Fix It: Check Power Supply and Door Panel

What You'll Need

• Flashlight

Steps

1. Turn off power at the breaker and shut off the gas supply valve Locate the circuit breaker for your furnace in the electrical panel and flip it to OFF. Then find the gas shut-off valve on the gas line leading to the furnace and turn it to the closed position. If you smell gas at any point, leave the house immediately and call your gas company from outside.
2. Check the circuit breaker Look at your home's electrical panel. Find the breaker labeled for the furnace or HVAC system. If it has tripped (sitting in the middle position or at OFF), flip it fully to OFF first, then back to ON. A breaker can look like it's on but still be tripped — push it firmly to the OFF position and then back to ON.
3. Check the furnace power switch Most furnaces have a dedicated power switch mounted on or near the unit. It looks like a standard light switch. Make sure it is in the ON position. This switch is sometimes accidentally bumped off during maintenance or storage activities near the furnace.
4. Verify the door panel is fully seated The Carrier 59SC2B has a door safety switch that cuts power to the control board when the front door panel is removed or not properly latched. Push the door panel firmly into place until you hear or feel it click. The panel must fully engage the safety switch for the board to receive power.
5. Restore power and check the LED Turn the gas supply valve back to the open position, then turn on the breaker. Wait 30 seconds and look through the viewing window on the furnace door. If the amber LED is now glowing steadily (continuous on), power has been restored and the furnace is in normal standby mode.

When to Call a Professional

Contact a licensed HVAC technician if:

• The breaker trips again immediately after you reset it
• The power switch and breaker are both on, the door panel is fully seated, and the LED is still off
• You notice a burning smell or scorch marks near the furnace or electrical panel
• The furnace has experienced a power surge (e.g., after a lightning strike or outage)
• You suspect a failed transformer or blown fuse on the control board