You can try the head replacement mode ,take out the left head,clean contacts on the head and on the head board.Put the head back in ,and power up.See if it solves the issue.If not ,than probably ,something else is going on ,or you just need a new head.What is the life time of the heads??The purge unit sucks ink out of the head ,in a (one of the) cleaning cycle(s).Check the left head pad ,for dried ink.As a precaution ,when taking the head out ,and cleaning the contacts in the printer ,disconnect the power cord from the mains.If you need more help you can get ipf500 service manual from the below link:
http://goo.gl/ngye6LGood luck
