Hydraulically controlled instantaneous water heater with tubular heating system and shower set for supplying hot water to a shower. The appliance is conveniently switched on and off via the On/Off knob. The required hot-water temperature is set via the flow rate and heating power. The heating power can be switched off and set to three different levels on the upper knob, while the flow rate is adjusted by means of the middle knob. A thermal cutout prevents overheating.