Flued gas boilers are gas boilers that take the oxygen in our habitat, combine it with has and send the waste gas to the flue. Technically, this is the most important detail of hermetic gas boilers. Flued gas boilers are far weaker than hermetic gas boilers in terms of security. In order to avoid any security gaps, many companies have placed sensors on these flues. These sensors shut down the gas boiler when the temperature of flue gas exceeds 100 degrees. Deaths due to flue accidents have increased and keep increasing in Turkey. When the chimney backfires, an extreme temperature rise occurs inside the chimney. There are sensors inside the chimney, which sense such temperature rise and automatically shut down the gas boiler.