Error Code 12
Info

Bryant 340MAV Error Code 12: Blower On After Power Up

TL;DR
Code 12 means the blower ran for 90 seconds after power-up because a heating call was active when power was restored. This is normal protective behavior.
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 12 Mean?

Status code 12 on the Bryant 340MAV is displayed when the circulating blower runs for 90 seconds immediately after the furnace is powered on. This occurs under two specific conditions: the unit was powered up while a call for heat was already active (R-W/W1 thermostat contacts closed), or the R-W/W1 contacts opened during a blower on-delay period.

The 90-second blower run is a protective measure in the integrated furnace control. When power is restored during an active heating call, the control cannot immediately verify whether the heat exchanger is already hot from a previous cycle before the outage. Running the blower for 90 seconds clears residual heat and allows the board to perform startup checks from a known thermal state before attempting ignition.

This code clears on its own once the blower cycle completes and the furnace proceeds through its normal startup sequence. It does not indicate a fault.

Contact a licensed HVAC technician if any of these apply:

Sources

  1. Bryant 340MAV J-Series Installation and Service Instructions

✓ Verified against manufacturer service manual — March 2026