Working on a Lennox Rooftop that keeps cycling on and off in heat mode.As soon as the blower kicks on,the flame shuts down.Draft inducer stays running, and the prossess starts allover again. When I opened the cover to inspect the heat X the unit will stay running.Even after Iput the cover back on the heat X it will keep running. But when I shut off the disconect and turn it back on (to simulate it being satisfied)The problem starts allover again. Iam thinking faulty high limit switch but when it stays running after the door comes off and then reinstsalled, I run out of answers. Any suggestions from anyone??