It is not the motor or the pressure switch. It sounds like its in the gas valve circuit. I belive it is timeing out when it does not prove flame. Do you have a meter? Check and see if you are getting 24V across the gas valve. It will happen after the ignitor fires. If so ohm out the gas valve if it is open then it's bad. If you do not have 24V at the valve back step to the board/relay and find the open switch. Remember rollout and high limit switches are there for a reason.
