I have a Bryant 350MAV gas furnace. I am getting a fault code 12. Can anyone tell me what a fault code 12 means?

Code 12 simply means that there was a call for heat when the power was turned on to the furnace. It is not a fault code, but a information code.

I keep getting the same code 12, the furnace shuts down and will not restart until I turn the power off then back on. Any info would be great. I have a bryant plus 90i, installed in 2002.

Try cleaning the flame sensor. It is a remote possibility it is going into lock out on flame proving.

I will do that, could you please tell me where that sensor is? Also the model of my furnace is a 355MAV. The problem seems to occur more often when the filter is installed, if I remove the filter, it seems to work better. Also on the back of the front panel, there is a list of codes and the descriptions. It says that code 12 means that there is a blower calibration lockout.

That's odd. Code 12 is nowhere near a blower-related issue in the manual for the 355MAV series "H" & "I". Codes 15 & 41 are blower faults, 42 is inducer fault. What is the complete product # ? The sensor is to the left of the intake air collector on upflow installations. Tricky to get to if the intake pipe enters from the left side.

Product # is ZI355MAV060100FFKA. The code description also says to refer to code #44. Code 44's description says it is a blower calibration fault. Everything seems to indicate that there is some kind of resistance in the air intake, but I have installed a new filter and checked the intake registers. It definitely happens more often when the filter is installed. I have been reading through the manual that came with the unit and I am wondering if my installer could have set up the continuous fan switches wrong. I can follow the instructions to fix, but I do not know how to determine the desired continuous fan airflow. Hope you can follow that.

What type of filter are you using? The resistance, even when new, may be excessive. You may also have a supply restriction, such as a clogged evaporator, and removing the filter lowers the total resistance below the threshold for blower fault. The continuous fan CFM selection is based on the desired continuous airflow, and is typically set fairly low. While the A/C CFM selection must be set according to the tonnage of the A/C system, it has no impact on heating CFM. Switch settings on chart are based on 400 CFM per ton.