Some numpty trade professional has capped off the vent to a copper cylinder and blown it up. Together with the house.
See here;
http://www.hpmmag.com/health-and-safety/plumber-fined-just-500-despite-causing-an-explosion
See here;
http://www.hpmmag.com/health-and-safety/plumber-fined-just-500-despite-causing-an-explosion