Due to the difficult availability in obtaining spare parts and too high maintenance costs the Deutsche Bahn AG decided to replace all heat regulators in the Bvmz coaches with new and improved SMA heat regulators. The heat regulator is used to regulate the temperature inside the coach and to control the different heater mats positioned in the ventilation ducts and in the floor of the coach vestibule. The fixing and the geometric dimensions of the heat regulator are adjusted to the available mounting space. The new heat regulators can therefore be installed in the existing switch cabinets of the Bvmz coaches without mechanical adjustments.