Carrier Furnace Code 24
Hard lockoutShown as: 2 short flashes, 4 long flashes
The 3-amp secondary voltage fuse on the control board is blown, which means there is a short somewhere in the 24 V low-voltage wiring.
Manual wording: “24 SECONDARY VOLTAGE FUSE IS OPEN - Check for: - Short circuit in secondary voltage (24V) wiring including thermostat leads.”
Documented for: 58SC0A, 58MCB, 58MVP, 58UVB
Likely causes, most common first
- Short circuit in the 24 VAC secondary wiring, including the thermostat leads
When to call a technician
Replacing the fuse without finding the short just blows the new fuse. A technician needs to isolate the shorted thermostat or accessory wire.
A Carrier furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- Installation, Start-Up, Operating and Service and Maintenance Instructions - 58SC0A/58SC1A (Carrier, 58SC0A/58SC1A single-stage 4-way multipoise condensing gas furnace) · checked 2026-08-25
- Troubleshooting Guide - Variable Speed, Two-Stage Gas Furnaces (Form 58-06T) (Carrier, 58MVP, 58UVB and other Carrier variable-speed two-stage gas furnaces (replaces 58MVP-10SM)) · checked 2026-08-25
- 58MCB 4-Way Multipoise Fixed-Capacity Condensing Gas Furnace - Service Manual (Carrier, 58MCB single-stage condensing gas furnace) · checked 2026-08-25