In some examples, a method includes, in response to a fluid firing unit being operated according to a normal printing mode, applying a first voltage to the fluid firing unit to fire the fluid firing unit during a printing operation. The method further includes determining, using a sensor, whether a predetermined condition is met, and in response to determining that the predetermined condition is met, operating the fluid firing unit according to a recovery mode in which a second voltage higher than the first voltage is applied to the fluid firing unit to clean the fluid firing unit.