While it may seem obvious, the first step to working your tankless water heater is simply to turn it on. You want to make sure that hot water is flowing through your pipes, this means turning on the hot water. Of course, today that isn’t always a simple explanation. If you have a single knob, be sure to turn it towards the hot water. If you have dual knobs, it’s much simpler. Locate the hot water knob, and turn it to allow the hot water to flow through.