A cap is positioned to contact a printhead when the printhead is not ejecting liquid ink. The cap and the printhead create a sealed space adjacent printhead nozzles when contacting each other. A heated evaporator is connected to the cap and is adapted to evaporate an ink-compatible liquid to form a water and/or solvent vapor and supply the water and/or solvent vapor to the sealed space to protect the liquid ink in the nozzles. An insulator thermally insulates the heated evaporator from the printhead. This prevents the ink in the nozzles from drying and prevents the nozzles from clogging.