Hi Graham,
Thank you for your question. I think you will find this thread helpful. Hopefully your unit is less than 2 years old, otherwise it looks like there are still some ways to go about getting your faulty printhead replaced:
http://www.fixyourownprinter.com/forums/inkjet/25785
Good luck! Please let me know if I can assist further and I would be happy to do so! Thanks again,
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Computer Software Engineer
Software Engineer and Support Professional