I have a reznor udas. Just installed. It kept cycling on/off on the way up, slowly, to temp. They spec type III piping - seamless stainless steel, so I used z-flex. I thought it would be wise to use an appliance adapter with backflow flap preventer to connect to the exhaust. This was the problem. Do not use a backflow preventer. I switched to one without the backflow preventer and the cycling stopped. The rotating flap of the backflow preventer had enough resistance to alter the combustion air switch in the Reznor.
Lesson learned. Hopefully this will help someone else!
Tom
Lesson learned. Hopefully this will help someone else!
Tom