Bryant 355MAV Error Code 12: Blower On After Power Up
What Does Code 12 Mean?
Status code 12 on the Bryant 355MAV indicates that the blower motor turned on for approximately 90 seconds after power was applied to the furnace. This happens in two specific scenarios: either the furnace was powered up while the thermostat was actively calling for heat (R-W/W1 circuit closed), or the thermostat call ended during the blower on-delay period after power was restored.
This 90-second blower run is a deliberate safety feature, not a malfunction. When the furnace receives power during an active heating demand, the control board runs the blower briefly before attempting to start a normal heating cycle. This ensures any residual heat in the heat exchanger is safely dissipated and allows the control to properly initialize before beginning the ignition sequence.
You are most likely to see this code after a power outage, after flipping the furnace circuit breaker, or after the furnace door switch is reengaged. After the 90-second blower run completes, the furnace will proceed with normal operation. No action is needed — the code is simply documenting what happened.
- The blower runs continuously and does not stop after 90 seconds, or the furnace fails to begin a normal heating cycle after the initial blower run
✓ Verified against manufacturer service manual — March 2026