Error Code 21
Bryant 355MAV Error Code 21: Gas Heating Lockout
TL;DR
Main gas valve relay on the variable speed furnace control is stuck closed or there is a miswire/short to gas valve wiring. BLUE wire goes to gas valve M terminal, GREEN/YELLOW wire goes to gas valve C terminal. Control will NOT auto reset. 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 21 Mean?
Main gas valve relay on the variable speed furnace control is stuck closed or there is a miswire/short to gas valve wiring. BLUE wire goes to gas valve M terminal, GREEN/YELLOW wire goes to gas valve C terminal. Control will NOT auto reset.
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