When my furnace has warmed up the house and turns off for a bit it struggles to turn back on. While the furnace is cold I can look into the combustion chamber and notice the flame is acting like something is trying to blowing it out, causing a flame sensor fault and shutting down the system. Now I know its not a cracked heat exchanger because the fan is not running while this happens, and once it has warmed up the furnace a little bit it stops trying to go out. Furnace is an evcon DGAT070BDD. I noticed that this first only happened on a rainy days, but now is a common occurrence if the furnace has not needed to run as much. Any help would be appreciated!