Updated 2026-06-25

Carrier Furnace Code 24: What It Means & How to Fix It

Compiled & reviewed by Nikolai Tsyrenov · Updated 2026-06-25 · confidence: high

What does Carrier furnace code 24 mean?

Secondary-voltage fuse is open — the 3-amp control-board fuse has blown due to a short in the low-voltage (24V) wiring. Most often caused by The 3-amp control-board fuse blew due to a short in the 24V wiring.

What Carrier furnace code 24 means

Secondary-voltage fuse is open — the 3-amp control-board fuse has blown due to a short in the low-voltage (24V) wiring.

Common causes

Homeowner-safe steps to try

  1. Turn the furnace power OFF at the switch and breaker before doing anything
  2. Visually inspect any low-voltage thermostat wiring you can safely see for obvious pinched or damaged spots
  3. If you recently installed a new thermostat or accessory, double-check it was wired exactly per its instructions
  4. Do NOT replace the board fuse repeatedly or jump it out — the short must be found and corrected first

When to call a licensed HVAC technician

If the basic checks below don't clear the code, the fault recurs, or anything involves the gas valve, burners, flame sensor or wiring, stop and book a licensed HVAC technician. Repairs to the combustion or gas system are not DIY.

⚠️ Safety first. Gas furnaces burn fuel and produce combustion gases. If you ever smell gas (a rotten-egg or sulfur odor), hear hissing, or your carbon-monoxide alarm sounds, do not touch light switches, thermostats, or the furnace — leave the home immediately and call your gas utility's emergency line or 911 from outside. Homeowners should limit themselves to simple, safe steps: setting the thermostat, checking and replacing the air filter, confirming the furnace switch and breaker are on, keeping supply registers and return grilles open, and clearing snow, ice, or debris from outdoor vent and intake terminations. Never bypass, jumper, or reset safety switches (limit, flame-rollout, or pressure switches), never open the gas valve or burner compartment, and never attempt combustion, electrical, or control-board repairs yourself. Error codes point toward a problem but are not a substitute for proper diagnosis — when in doubt, turn the system off and call a licensed HVAC technician. Keep working carbon-monoxide detectors on every level of your home.
When to call a pro: Call a licensed HVAC technician to locate and repair the short and fit the correct fuse — repeatedly replacing a blown fuse without fixing the short can damage the control board.

Carrier furnace code 24 FAQ

What does Carrier furnace code 24 mean?
Secondary-voltage fuse is open — the 3-amp control-board fuse has blown due to a short in the low-voltage (24V) wiring.
What causes Carrier furnace code 24?
Common causes: The 3-amp control-board fuse blew due to a short in the 24V wiring; A pinched or chafed thermostat/accessory wire shorting against metal; A shorted component (transformer, valve, or accessory) on the 24V circuit; A wiring/installation error during recent service or thermostat replacement.
Can I fix Carrier furnace code 24 myself?
You can safely try: Turn the furnace power OFF at the switch and breaker before doing anything; Visually inspect any low-voltage thermostat wiring you can safely see for obvious pinched or damaged spots; If you recently installed a new thermostat or accessory, double-check it was wired exactly per its instructions; Do NOT replace the board fuse repeatedly or jump it out — the short must be found and corrected first. Call a licensed HVAC technician to locate and repair the short and fit the correct fuse — repeatedly replacing a blown fuse without fixing the short can damage the control board.

Other Carrier furnace codes

Carrier Code 11No previous code stored — the control has no fCarrier Code 12Blower on after power up — the blower runs forCarrier Code 13Limit circuit lockout — the lockout version ofCarrier Code 25Model-selection or setup error — the control bCarrier Code 31Pressure switch or relay did not close, or reoCarrier Code 32Low-heat pressure switch did not close, or reoCarrier Code 33Limit circuit fault — the high-limit or flame-Carrier Code 34Ignition-proving fault — flame was not sensed,

All Carrier furnace codes →

Sources: shareddocs.com · manualslib.com. General information for homeowners, not professional advice — confirm against your furnace's manual and a licensed technician.