Well, the saga goes on.The MG3530 refused to print the blue again so I soaked the print head overnight and ran a clean and a deep clean cycle. It now works. It's clear to me, however, that there is a real problem with this print head. I now have two options: I can buy a new print head from Amazon (the cheapest I could find anywhere on the net) for £74 or I can buy a brand new MG3250 for £47. That means I could use my stock of ink and, if I wanted, exchange the print heads as they are compatible. Guess which I'll go for?!!