Review the folowing information:
Try to exchanging the hoses connected under the burner. The 2 cables might give signal interruptions when they touch eachother, make sure this is not the problem.
Remove the plastic straps securing the hoses leading from the burner to the burner controller. It could be that they interrupt the flow.
Remove the filter and see if now lights, if lights without the filter, means that the filter is dirty. Follow the steps on the below file to clean the burner and the filter.
Measure the pre pressure to the roaster. (share to us this information)
If you have reviewed each of the above points and nothing has worked, I suggest you order the following parts:
Burner controller
Ignition cables
Ignition pens
-If you replace the burner controller, make sure that the serial number match with the previous one.
Burner controller is not same model for smaller roasters than for W30.
-If you changed the ignition pens make sure that the possition looks as the previus ones.