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Back to all 58SB1 Comfort™ 80 Low NOx Gas Furnace error codes

Carrier 58SB1 Comfort™ 80 Low NOx Gas Furnace 24 troubleshooting

Secondary voltage fuse is open. Use this page to document the issue and prepare for service. GreenFlow should handle diagnosis for electrical, refrigerant, lockout, or recurring conditions.

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What the code means

24: Secondary voltage fuse is open

The furnace control is reporting that the secondary-voltage fuse is open.

System area
Low-voltage control circuit
Service level
Call GreenFlow

Safe checks before calling

  • Confirm the thermostat or controller is powered, set correctly, and calling for heating or cooling.
  • Check filters, return-air grilles, supply registers, and visible airflow paths that can be reached without opening equipment panels.
  • Look for visible outdoor-unit or rooftop obstructions, debris, snow, ice, or blocked clearances from a safe location only.
  • Take photos of the displayed code or LED pattern, equipment nameplate, thermostat or controller, and the surrounding equipment area before scheduling service.

When to stop and call GreenFlow

Call GreenFlow if the code repeats, the unit is locked out, heating or cooling is not restored, there is flame, gas, electrical, refrigerant, pressure, compressor, fan-motor, rooftop-access, or warranty-related concern, or any troubleshooting would require opening equipment panels.

Share the visible code, model and serial number if available, photos, current symptoms, and whether the issue affects heating, cooling, or both.

24 questions

What does 24 mean on a Carrier 58SB1 Comfort™ 80 Low NOx Gas Furnace?

The furnace control is reporting that the secondary-voltage fuse is open.

What should I safely check before scheduling service?

Confirm thermostat or controller status, check filters and visible airflow restrictions, look for outdoor-unit or rooftop obstructions from a safe location, and take photos of the code or LED pattern and nameplate. Do not open electrical, gas, refrigerant, or rooftop control compartments.

When should GreenFlow handle this code?

Call GreenFlow if the code repeats, the unit is locked out, heating or cooling is not restored, there is flame, gas, electrical, refrigerant, pressure, compressor, fan-motor, rooftop-access, or warranty-related concern, or any troubleshooting would require opening equipment panels.

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