Heater (46, 66) comprising several heat tubes filled with a working medium, extending preferably parallel or substantially parallel and each having a first end and a second end, and a heat source thermally coupled to the first and/or second ends (20, 22) of the heat tubes, the first ends of the heat tubes being designed open and fluidically connected to a first transverse connection tube and the second ends of the heat tubes being designed open and fluidically connected to a second transverse connection tube, the heat tubes and the transverse connection tubes (24, 26) forming a common cavity filled with the working medium, and the first transverse connection tube being thermally coupled to the heat source (16, 102) to receive heat from the heat source, wherein the heat source is a heating tube through which a gaseous or liquid heating medium can flow, the heating tube being arranged coaxially in the first transverse connection tube along a longitudinal axis and being surrounded by the working medium, characterized in, that connectors (32, 34) of the heating tube are connected to the first transverse connection tube at end face in pressure-tight and fluid-tight manner, that the heater (46; 66) has a connection system (48; 70) with a flow connection (50; 72) and a return connection (62; 86), wherein the flow being connected via a first bypass tube (52; 74) to a control valve (54; 76) which is coupled to a connector (56; 78) projecting at an end face from the second transverse connection tube and that a second bypass tube (58; 80) extends from the control valve (54; 76) preferably parallel to the first bypass tube, is in fluidic connection to the heating tube and is coupled to the return connection (62; 86). several heat tubes filled with a working medium, extending preferably parallel or substantially parallel and each having a first end and a second end, and a heat source thermally coupled to the first and/or second ends (20, 22) of the heat tubes, the first ends of the heat tubes being designed open and fluidically connected to a first transverse connection tube and the second ends of the heat tubes being designed open and fluidically connected to a second transverse connection tube, the heat tubes and the transverse connection tubes (24, 26) forming a common cavity filled with the working medium, and the first transverse connection tube being thermally coupled to the heat source (16, 102) to receive heat from the heat source, wherein the heat source is a heating tube through which a gaseous or liquid heating medium can flow, the heating tube being arranged coaxially in the first transverse connection tube along a longitudinal axis and being surrounded by the working medium, characterized in, that connectors (32, 34) of the heating tube are connected to the first transverse connection tube at end face in pressure-tight and fluid-tight manner, that the heater (46; 66) has a connection system (48; 70) with a flow connection (50; 72) and a return connection (62; 86), wherein the flow being connected via a first bypass tube (52; 74) to a control valve (54; 76) which is coupled to a connector (56; 78) projecting at an end face from the second transverse connection tube and that a second bypass tube (58; 80) extends from the control valve (54; 76) preferably parallel to the first bypass tube, is in fluidic connection to the heating tube and is coupled to the return connection (62; 86).