I've got the same issue going on here. I don't know if it is a vacuum issue or switch issue. I have to squeeze the tube closest to the sensor to get it to work . If you find a solution please share! Thanks!
I had to blow out the intake and exaust piping. Somehow they were plugged and it fired right up after I did that. I called my installer and he helped me on the phone instead of charging a service call! Thanks for your info. It is appreciated, Jim.