Lexmark 600 and I always use the Lexmark ink replacements. It says wipe the printhead contacts using a clean lint free cloth. ,then replace printhead ,close the latch until it clicks and close the printer.
1 year old, still under guarantee from pcworld.
removed the printhead as instructed in the manual after lifting the latch,wiped the printhead contacts using a lint free cloth, then reinsert print head closed the latch until clicks, closed the printer. if still showing printhead error, then contact tech support.