Trane xb90 does not light all burners fast enough to satisfy flame sensor which is on the last burner so the unit cycles out and after three times it locks out until you kill the power to reset the control board. Usually the first couple of burners will light and stay lit maybe a second then cycles out. Occasionally it will light all of them and in a second or less. I used to work on furnaces back in the day when for the most part you had standing pilots and no control boards. I did change the glow coil because used to if they had some age on them they would begin to rob the gas valve of enough millivolts to keep it from opening.

A good place to start would be to clean the cross igniter bar on the burner assembly. This is usually a small channel that allows gas to flow from one burner to the next to ignite all burners. It many times becomes plugged with dust or corrosion and can be cleaned with a wire brush and a little compressed air. On many units this requires removing the burner assembly for access.

A good place to start would be to clean the cross igniter bar on the burner assembly. This is usually a small channel that allows gas to flow from one burner to the next to ignite all burners. It many times becomes plugged with dust or corrosion and can be cleaned with a wire brush and a little compressed air. On many units this requires removing the burner assembly for access.

If I was a betting man I would bet that you are exactly right. Here in Tennessee it is just now gettting cold enough at night to run the furnace and it has set all summer. I will have to remove the burner assembly to get to it but I sure appreciate your imput. Thanks bunches

Good luck and please let me know the outcome. Take care.