What causes an electric water heater reset button to trip? What are some troubleshooting tips to fix it?

Hot water heaters are often fitted with a backup thermostat that trips if the contacts freeze on the main thermostat. On common "quick recovery" water heaters there are two heating elements, one above the other. The upper thermostat feeds the upper element, or passes power to the lower thermostat and the lower element.

The lower element is nearer the outlet of the tube bringing in cold water and so it does most of the work. Only when most of the hot water in the tank is used up does the upper element take over and heat just the upper third or so, to give a "quick recovery." It is not uncommon for the lower thermostat to fail, but you should also check the element to see if it has failed with a short to the case. When an element has failed, it may create a circuit from the side of the line that does not go through the thermostat Through part of the element and on to ground.

Something is allowing the water to get to hot, tripping the safety thermostat, or that thermostat is tripping at too low a temperature. Sometimes a thermostat can be freed by twisting the setting adjustment back forth to the stops before setting back to the appropriate setting. This may get you by till you can replace the thermostat.