NickTech said:well if you need to remove the air intake to the burner, it sounds like it may be a restriction problem. are you sure its the air intake, how many pipes are there. if just one then its the exaust. in any event there may be a design/install problem with the size of the pipe.send a pic if possible.
check out pg. 7 thru 11 on that site i sent in the other post for polaris.
NickTech said:perhaps the difference with it running during the day is air temp. the colder nights may be freezing something causing a restriction, however there should sensor for that. being that unit is not shutting down, only running rough i would think that was it. the only thing i can think of is the air mass at night is heavier and denser with alot more oxygen and cause a bad fuel air mix.