All of my windows open properly inwards from the side hinges. But some do not "tilt" i.e. open properly on BOTH bottom hinges, only one. What can I do?
Without actually looking at the windows first hand, it is difficult to know why they are not tilting. The height of the sash might need adjusting (remove cover from bottom hinge, adjust up or down with an allen key), keeps might need moving, glass might need re-packing, gearing parts might need to be replaced if broken.
It might be advisable to call out a local double glazing repair company, look in yellow pages or in yell.com under "double glazing repairs". Tilt n Turn windows are quite complicated and often best left to those with the know how.