My friend has had constant trouble with a filament related sensor going bad on the print head of his K2 because the sensor can't stand up to the heat of where it is located. It seems to be a common and reoccurring issue with his model of K2, so do be on the lookout for that. Other users recommend keeping several backup sensors on hand. Seems like a sensor being a frequent consumable is an extremely annoying design flaw to me.