Heater comprising a central-heating line, in which liquid circulates, and at least one safety drain valve , which is connected to the central-heating line and with which the function of a safety valve and the function of a drain valve are combined in a single valve, wherein the safety drain valve comprises at least one connecting pipe , connected to the central-heating line, at least one drain pipe , connected to the connecting pipe , at least one adjustment pipe , arranged between the connecting pipe and the drain pipe , and at least one valve element , arranged in the safety drain valve , which comprises at least one spring arranged on the connecting pipe for closing the throughflow path of the connecting pipe , this pushing at least one first wall to at least one abutment wall , wherein the spring is arranged between at least one second wall and the first wall , the second wall is connected to the drain pipe , and the second wall and the first wall are configured in such a way as to move towards one another or away from one another, wherein the spring is configured in such a way that, below a predefined critical liquid-pressure value, it is not compressed, the first wall abuts against the abutment wall and no passage of liquid is permitted; and, if the liquid pressure exceeds the critical liquid-pressure value, the spring is compressed, with liquid passing to the drain pipe, wherein the drain pipe comprises at least one movement lever which is arranged at least partially in a movement channel on the outer periphery of the adjustment tube , the movement channel has the shape of a spiral, and the movement lever is configured in such a way as to move between at least two ends of the movement channel , wherein the spring is configured in such a way that it presses the first wall to the abutment wall , when the movement lever is in the vicinity of the first end , with no fluid passing from the connecting pipe to the drain pipe ; and wherein, if the movement lever is in the vicinity of the second end , the spring is compressed, the first wall and the second wall approach one other and liquid can pass from the connecting pipe into the drain pipe . wherein the spring is arranged between at least one second wall and the first wall , the second wall is connected to the drain pipe , and the second wall and the first wall are configured in such a way as to move towards one another or away from one another, wherein the spring is configured in such a way that, below a predefined critical liquid-pressure value, it is not compressed, the first wall abuts against the abutment wall and no passage of liquid is permitted; and, if the liquid pressure exceeds the critical liquid-pressure value, the spring is compressed, with liquid passing to the drain pipe, wherein the drain pipe comprises at least one movement lever which is arranged at least partially in a movement channel on the outer periphery of the adjustment tube , the movement channel has the shape of a spiral, and the movement lever is configured in such a way as to move between at least two ends of the movement channel , wherein the spring is configured in such a way that it presses the first wall to the abutment wall , when the movement lever is in the vicinity of the first end , with no fluid passing from the connecting pipe to the drain pipe ; and wherein, if the movement lever is in the vicinity of the second end , the spring is compressed, the first wall and the second wall approach one other and liquid can pass from the connecting pipe into the drain pipe . <EOS>