potterton profile 80NG boiler seems to blow main fuse ?

Our main fuse (for boiler, outside socket and one internal socket, as far as we know?!) has blown for about 5th time in last few weeks. Only have the HW on at the moment noticed today after changing the fuse again! boiler didn't heat to high enough temp before it must have turned off. It turned on again as I ran some water close to temp at least but sometime after that it blew a fuse again? Has anyone any ideas what would cause it to blow fuse? I think most its most likely the boiler as outside socket looks OK and not using it or the other one indoors. Any things to check or ideas . Thank you for your time.