Iron

Greetings, I am having trouble figuring out what to with my UM2 clogging issues. Even doing atomic cleanings I still seem to have a consonantly decreasing print time before needing to clean it again (now about 10 hours before I have a clog kill a print). I even switched the nozzle with a brand new one and the issue continued. What could be causing such extreme clogging issues? How often do you have to clean you print head? I'm using pla at 220 if it matters. Thanks!