Error Code Code 21
Carrier 58MVP Error Code Code 21: Invalid Model Selection
TL;DR
Indicates the model plug (personality connector PL5) is missing or incorrect. The furnace will operate acceptably; however, a model selection circuit failure has occurred and the furnace control board is defaulting to last valid model selection. Board replacement is recommended but not necessary. This fault code will flash continuously. Disclaimer
This article is for informational purposes only and does not guarantee the accuracy or completeness of the information provided. Always turn off power and gas supply before attempting any repairs. If you smell gas, leave immediately and call your gas company. Consult a licensed HVAC technician for diagnosis and repair. Any actions taken based on this information are at your own risk. What Does Code Code 21 Mean?
Indicates the model plug (personality connector PL5) is missing or incorrect. The furnace will operate acceptably; however, a model selection circuit failure has occurred and the furnace control board is defaulting to last valid model selection. Board replacement is recommended but not necessary. This fault code will flash continuously.
Common Causes
When to Call a Professional
Contact a licensed HVAC technician if:
- Basic troubleshooting did not resolve the error
- You smell gas at any point during the process
- You are not comfortable working around gas lines or electrical components
- The unit needs a gas valve, control board, or motor replacement