Carrier Error Code 21: Gas Heating Lockout
Warning: A Carrier 21 error code indicates a gas heating lockout. This could mean a dangerous gas leak or carbon monoxide risk. Shut down your system immediately.
How to Fix Carrier Code 21
- Step 1: Turn off the furnace at the breaker box to prevent further gas accumulation.
- Step 2: Ensure all gas appliances are off and the gas meter is shut off.
- Step 3: Immediately call a licensed HVAC technician and your gas company to report a possible gas leak.
How to Reset Carrier Code 21
- 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.
What does 21 mean?
The Carrier 21 error code, also known as a gas heating lockout, signals that your furnace has tried to ignite the gas multiple times but failed. After several unsuccessful attempts, the system locks itself down as a safety precaution. This is often due to a problem in the ignition sequence or a detected hazard. It's important to address this issue promptly to restore heating and ensure your safety. Continuing to run a system with a lockout can potentially lead to dangerous conditions or further damage to the unit. Contact a qualified HVAC technician to diagnose and repair the problem.
Affected Models
- Performance Series Furnace
- Comfort Series Furnace
- Infinity Series Furnace
- Performance Series
- Base Series Furnace
- Performance Boost Furnace
- Performance Boost 95 Furnace
- WeatherMaker 8000
- WeatherMaker 9300
- Infinity 80
- WeatherMaker Furnace
- 24ABC6 Air Conditioner
- 25HBC5 Heat Pump
- Performance Series Heat Pump
- Infinity Series
- Base Series
- Comfort Series
- Infinity Series Heat Pump
- Comfort Series Heat Pump
- Infinity 20 Heat Pump with Greenspeed Intelligence
- Comfort 80 Gas Furnace
Replacement Parts
| Part | OEM Number | Est. Cost |
|---|---|---|
| Hot Surface Igniter | — | — |
| Gas Valve | — | — |
| Flame Sensor | — | — |
Related Codes on Same Models
| Code | Description | Severity |
|---|---|---|
| 11 | No Previous Error | Info |
| 12 | Blower On After Power Up | Warning |
| 13 | Limit/Rollout Fault | Critical |
| 14 | Ignition Lockout | Critical |
| 22 | Abnormal Flame | Critical |
| 23 | Pressure Switch Fault | Warning |
| 24 | Secondary Voltage Fuse | Warning |
| 31 | High Stage Pressure Fault | Warning |
| 32 | Low Flame Sense | Warning |
| 33 | Limit/Rollout Switch Lockout | Critical |