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.