Carrier Error Code 24: Secondary Voltage Fuse
LED Blink Pattern
2 short blinks, 4 long blinks.
How to Fix Carrier Code 24
- Step 1: Check your thermostat batteries. Replace them if they are old or weak.
- Step 2: Inspect the wiring connections at the thermostat. Make sure all wires are securely connected.
- Step 3: Reset the system by turning off the power at the breaker for 5 minutes, then turn it back on. If the error returns, call a qualified HVAC technician.
How to Reset Carrier Code 24
- Turn off the furnace power switch, usually located on or near the unit.
- Turn off the circuit breaker for the furnace. Wait 30 seconds.
- Restore power at the breaker and flip the furnace switch back on.
- Set the thermostat to call for heat. If the error code returns after 2-3 ignition attempts, the fault requires repair.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does Carrier Error Code 24 Mean?
The Carrier error code 24, or a blinking LED pattern of 2 long flashes followed by 4 short flashes, indicates a problem with the secondary voltage fuse. This fuse protects the low-voltage components of your Carrier system, such as the control board, sensors, and sometimes the thermostat. When this fuse blows, it means there's an overcurrent situation in the low-voltage circuit, which could be caused by a short circuit, a faulty component, or a wiring issue. The system will typically shut down to prevent further damage. Because this code relates to electrical components, it's important to have a qualified HVAC technician diagnose and repair the problem. They will be able to safely troubleshoot the electrical circuits, identify the cause of the blown fuse, and replace any faulty components. Attempting to fix this yourself without proper training and equipment could be dangerous and could potentially damage your system further.
Common Causes
- Short circuit in the low-voltage wiring
- Faulty transformer
- Defective control board
- Failed low-voltage component (e.g., inducer motor, blower motor)
- Loose or corroded wiring connections
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Fuse is blown | Measure voltage at the transformer secondary | 24 VAC |
| Voltage is present at the transformer | Check resistance of all low-voltage wiring runs to ground | OL (open circuit) |
| Wiring checks out | Disconnect components one by one and check resistance to ground after each disconnection | OL after disconnecting the faulty component |
Applicable Carrier Models
- 24ABC6 Air Conditioner(electric)
- 25HBC5 Heat Pump(electric)
- Base Series(gas)
- Base Series Furnace(gas)
- Comfort 80 Gas Furnace(gas)
- Comfort Series(electric)
- Comfort Series Furnace(gas)
- Comfort Series Heat Pump(electric)
- Infinity 20 Heat Pump with Greenspeed Intelligence(electric)
- Infinity 80(gas)
- Infinity Series(electric)
- Infinity Series Furnace(gas)
- Infinity Series Heat Pump(electric)
- Performance Boost 95 Furnace(gas)
- Performance Boost Furnace(gas)
- Performance Series(gas)
- Performance Series Furnace(gas)
- Performance Series Heat Pump(electric)
- WeatherMaker 8000(gas)
- WeatherMaker 9300(gas)
- WeatherMaker Furnace(gas)
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| 3 amp fuse | — | — | — |
| 24V Transformer | — | — | — |
| Integrated Control Board | — | — | — |
Related Codes on Same Models
Other codes that affect the same Carrier model families as 24.
| Code | Description | Severity |
|---|---|---|
| 12 | Blower On After Power Up | Warning |
| 13 | Limit/Rollout Fault | Critical |
| 14 | Ignition Lockout | Critical |
| 21 | Gas Heating Lockout | Critical |
| 22 | Abnormal Flame | Critical |
| 23 | Pressure Switch Fault | Warning |
| 31 | High Stage Pressure Fault | Warning |
| 32 | Low Flame Sense | Warning |
| 33 | Limit/Rollout Switch Lockout | Critical |
| 34 | Ignition/Flame Sense Fault | Warning |