I upgraded my iMac and MacBook Air to Yosemite. Since doing this, my HP 7510 – which worked perfectly before the upgrade – no longer works without a drawn-out workaround (switching the printer off after I’ve given the Print request, then switching it on again). Sometimes it prints out my request. Even if I try and print immediately after this, it won’t print. (It might if I switch the printer off and on again.) If I look at the print dialog box, it tells me ‘the printer is not connected’, and under that ‘PrintingLooking for printer’. This happens with my iMac and the MacBook Air. Ronnie Stuart You won’t like this, but I think you should just buy a new printer. I realise that this will seem defeatist, but consider the situation rationally. There is nothing wrong with your Mac – the fact that the problem is the same on two different computers is proof of that. So it’s either a driver compatibility issue or a hardware fault with the printer. The intermittent nature of the problem inclines me to suspect hardware, but it doesn’t really matter – the fix in both cases is to get a new printer. If you value your time at just minimum wage, then blowing £70 on a new printer, is the same as 10 hours spent on the phone to support phone lines and browsing the internet forums. I’d suggest the Epson Expression Home XP-422.