Abstract: A safety shut down warning assembly of the manual reset or recycling type installed at the lower section of a water heater storage vessel inside or outside the wall of the storage tank of the vessel to sense a predetermined increase in temperature above the normal operating temperature in the lower portion of the tank as the result of buildup of lime or other sediment in the bottom of the tank of the storage vessel. The sensing device is then activated by the increase in temperature to shut down the heating unit employed with the storage vessel to heat the water stored therein and/or turn on a warning light or other signal.