"sticky" gas water heater thermostat
Gas water heaters use a thermocouple, just like gas furnaces, to kill the trickle of gas to the pilot orifice if the pilot is lost for some reason or other.
The thermostat is a somewhat independent component. The thermostat may or may not work in the same way as the thermocouple, i.e. a bulb with a capillary tube operating like a long flexible mercury thermometer* and going to a pressure operated "valve handle", or a small temperature dependent voltage generating device that controls a small self contained electrical circuit.
*Also a version like a short fat thermometer at whose far end is the "valve handle" or a plunger valve for the gas.
If you are shopping for a water heater with digital temperature control, consider that some require AC power and won't give you hot water if there is a power failure. Kind of inconvenient after a big summer storm and you got all hot and sweaty cleaning up outside and now can't take a shower.
I don't believe that the digital water heaters do anything more about the hot water itself compared to the old fashioned thermostat gas valve kind. The digital models may have such features as allowing the water to cool down only during the day if no one is home, or programmable lower temperature for vacations, or remote control.
Last edited by AllanJ; 01-25-2008 at 09:12 AM.