i often use 600 grit sandpaper to get burnt plastic of the sides of my printer nozzle. By doing this filament is less likely to stick to nozzle and drag across your print. Of course you can always soak in Acetone however that is a long process of waiting.

There's multiple setting in firmware that causes the print head to disable at temperatures higher than 240ish. Go into the updated firmware supplied by seemecnc and in the master config file in Arduino use ctrl f to search "temp". youll notice some max settings are set to 240. change those to 270. even though he280 can go slighter higher im not familiar with any filaments that require that high of a temp.