Sounds like you have to replace your thermostats on the water heater.
Im not recommending you do bu this is how I troubleshoot water heaters.
If your water heater has stopped heating, begin troubleshooting at the fuse/breaker panel. Check the fuse/breaker to insure that you have current flowing to the water heater.
Check the fuse/breaker to insure that you have current flowing to the water heater. Next remove the top thermostat cover, and using a volt/ohm meter check for current on the thermostat terminals marked L1 and L2. If you have current there, push the red button labeled "Reset".
Next check for current on the heating element, if the water in the tank is cold you should have current there. If the water is cold and there is no current, then you have a bad thermostat. If the thermostat is good, turn off the electricity at the fuse/breaker panel and remove the wires from the heating element.
Using your ohm meter, test for continuity through the element itself by touching your test leads to both element screws at the same time. If you have no continuity the element is bad, however if you do have continuity you still need to do one more test.
Check each screw separately by touching one lead to the screw and the other to the water tank. You should have no continuity this way, unless the element is shorted out and you are reading through the water.
If you find all of the upper components in working order, reattach the wires to the element and replace the top cover. Then turn the electricity back on and perform these same checks on the lower components.
When you find the offending component, replace it.
If your water heater is more than 10 years old, I recommend replacing it. The efficiency of a new one will save you big bucks on your electric bill.
Allied Plumbing and Construction Company