How do I light the water heater when the gas has just been turned on at the cylinder? (It is an instantaneous water heater in a mobile home). I can do it by running the hot tap, turning the thermostat to medium, and turning and pressing the gas control valve/ignitor. But I'm concerned that this might be dangerous, since I am simultaneously lighting the pilot and the burner, as opposed to just the pilot. However, it seems not to work unless I turn the thermostat to medium.