IPhone 4s wifi stopped working after ios8 install

Hi I've owned an iPhone 4s for two trouble free years, however after installing ios8 I've lost my wifi (greyed out!). I have an appointment with the apple people next week, but I'm preparing myself for a battle because when I made the appointment the chap told me it was very unlikely to be an install problem and just a coincidence!!

Just for for the record I've tried all sorts of different remedies, the only one I'm unable to carry out is a compete reinstall as I can't switch off find my phone due to another problem I have with icloud passwords!

Thanks in anticipation