A tankless water heater comprising a bare wire heating element is disclosed which is connected to an electronic temperature control system. At least one sensor is furthermore connected to the electronic temperature control system. A fluid heating chamber is made of insulating non conductive material wherein the heating element is located. At least one switch is connected to at least one bare wire heating element and to a phase of an AC line. An electrode system and an electronic detecting circuit are interconnected. The electrode system is arranged in a fluid channel, in a short distance from the bare wire heating element which acts like electrode 1. The electrode 2 of the electrode system is made from a conductive tube material hydraulically connected to a throttle valve made from non conductive material to insulate the electrode 2 from the grounded collector. The electrode 2 is electrically connected to a electronic control system via a conductive material.