Autoglass replaced my screen just before Christmas but only half the heated screen worked so had to replace it again, which was done this week. Now it seems the rain sensor doesnt work as it did. It works but the screen needs to bee too wet to see through before the wipers start to work. That is with the variable speed at its fastest, at the slow end they don't even come on. Could this be the refitting of the sensor?

The sensor is clipped to the optical device which comes already bonded to the new screen. If you unclip the shroud around the mirror mounting you will see it (a rectangular box) and can check if it's clipped on properly. I think it should initialise on first use otherwise it may need the use of the dealer's computer to recalibrate. Should be covered if you are still in warranty.