hello I know pretty well the C3 plural, I am used to work on it. I read your problem, and the first things you have to do, is to reboot your roof computer. It isn't complicated to do, but it is a bite hard for me to explain it. So excuse my english mistakes...........so you have to check the roof system. first start your engine, secondly go down the roof completely you must go on the boot. thirdly go up the roof and when your roof is completely closed normally your switch must be completely turned and now the more important thing you have to push on the roof switch during 30 seconds and after this time you must hear a sound like a motor that move. and now I hope everything will goes well for your car boot. perhaps it could be an other problem on your car.. first you must try this, and we could try other things later.... good luck I leave below a picture of the roof switch I told you