My house has two identical Low boy furnaces with becket AFG burners and R7184B primary controls. Two years ago right after I moved in one furnace locked-out so I called service. He worked on it for quite a while and couldn't find anything wrong, but swapped out the R7184B with a R7184A and that worked and it has been working fine every since. Nevertheless, I have always wondered why.
Can you think of anything that would cause a system to run fine with a R7184A and not with a R7184B.