H2/H3 LED digital display series and H3 have the over-temperature protection and water shortage protection function, respectively. When the water temperature is over 35 C (98 F), the heating rod stops the work and the display screen blink E2. When the water temperature is below 34 C (94″F), the fault disappear and it shows normal. For H3, when the water level is lower the top detector of the heating rod, the heating rod shows E1 and flashes to alarm. After the rod is fully submerged, the fault disappears and it shows normal.