Abstract: In order to protect a boiler against overheating a boiler draft control device comprises a safety thermostat in addition to the regular control thermostat. The control thermostat is provided with a supporting tube in order to limit its length reduction in the event of its failure. The safety thermostat is designed in such a manner that its working element only provides a displacement when the control range of the control thermostat is exceeded. Furthermore the safety thermostat has a very steep displacement/temperature characteristic and its maximum stroke is equal or greater than the stroke being given by an operable control thermostat over its total control range. A latch means is provided to prevent that an air inlet flap closed according to the response of the safety thermostat may be opened again with the cooling down of the boiler.