Error Code Continuous OFF
High

Carrier 59SC5A Error Code Continuous OFF: No Power / Control Failure

TL;DR
Your Carrier 59SC5A has no power. The status LED is completely off. Check if the circuit breaker has tripped or if the furnace power switch has been turned off.
Disclaimer
This article is for informational purposes only and does not guarantee the accuracy or completeness of the information provided. Always turn off power and gas supply before attempting any repairs. If you smell gas, leave immediately and call your gas company. Consult a licensed HVAC technician for diagnosis and repair. Any actions taken based on this information are at your own risk.

What Does Code Continuous OFF Mean?

When the status LED on your Carrier 59SC5A control board is continuously off, it means the HK42FZ036 furnace control board is not receiving electrical power. The furnace cannot operate at all in this state because the control board manages every function from ignition to the blower motor.

The most common cause is a tripped circuit breaker or blown fuse at your electrical panel. The second most likely cause is the furnace power switch being turned off. This switch is typically a standard light switch located on or near the furnace and can easily be bumped to the off position.

If both the breaker and power switch are fine, the problem may be a faulty transformer or control board. The manual specifies checking for 115 VAC at L1 and L2, and 24 VAC at SEC-1 and SEC-2, but these measurements require specialized equipment and should be left to a professional.

Common Causes

Cause Likelihood DIY?
Tripped circuit breaker or blown fuse Most common ✓ DIY fix →
Power switch turned off Common ✓ DIY fix →
Faulty transformer or control board Uncommon ✗ Call a pro →

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

⚠ Safety First
Always turn off the furnace at the power switch or breaker and shut off the gas supply before beginning. Do not proceed if you smell gas — leave the area and call your gas company immediately.

What You'll Need

Steps

  1. Turn off power and gas supply as a precaution Before investigating, turn the gas shutoff valve near the furnace to the OFF position (perpendicular to the pipe). If you smell gas at any point, leave immediately and call your gas company.
  2. Check the circuit breaker Go to your home's main electrical panel and find the breaker labeled for the furnace or HVAC system. If it is in the middle (tripped) position, flip it fully to OFF first, then back to ON. Some panels have fuses instead of breakers — check if the furnace fuse is blown and replace it with one of the same amperage.
  3. Check the furnace power switch Look for a standard light switch on or near the furnace, usually on the side of the unit or on a nearby wall. Make sure it is in the ON position. This switch is easily mistaken for a regular room light switch and may have been turned off accidentally.
  4. Restore gas and verify power Turn the gas supply valve back to ON (parallel to the pipe). Check the furnace control board through the access panel — the LED should now be lit continuously on, indicating 24 VAC power and normal standby. Set your thermostat to call for heat and confirm the furnace starts.
How to Verify
The LED on the control board should be continuously on, indicating the control has 24 VAC power and is in normal standby mode. When the thermostat calls for heat, the furnace should start its normal ignition sequence.

When to Call a Professional

Contact a licensed HVAC technician if:

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Sources

  1. Carrier 59SC5A Installation, Start-Up, Operating and Service and Maintenance Instructions

✓ Verified against manufacturer service manual — March 2026