ipad and iphone cant find printer. Any suggestions?!

I have a brand new mfc j 4510 air printer. After a few initial teething problems it now works very well apart from not printing from either

ipad or iphone. I've tried all of apples suggestions ie firmware update, turning printer on and off etc all to no avail.

When trying to print I just get the message no airprinter found- the same problem comes using brothers app.

Any suggestions?