Disconnected Power or Gas
The cause often is simple, even thought this might seem like a major problem. Verify that the hot water heater is connected to a power supply and reset the circuit breaker as needed. Turn the main power on the hot water heater to "On" and make sure that the gas valve also is turned on. Check the hot water heater's thermostat and increase it, if necessary. Allow a few hours for the temperature to adjust.
Mineral Scale Buildup
If the hot water heater has power but is not supplying as much hot water as it should, this might indicate that the hot water heater needs to be drained. Disconnect its power and let the unit cool completely before turning off the water. Attach a hose to the drain valve and put the other end in a large bucket. Turn on a hot water faucet in the home and let the water drain. Turn the cold water valve on and off several times when the water has finished draining. When the water runs clear, disconnect the hose, turn on the water and restore power. Locate the temperature pressure relief valve and lift up or lower the handle to allow any excess water to drain from the overflow pipe.
Temperature Pressure Relief Valve Problems
Problems with the temperature pressure relief valve can cause leaking and other problems. The temperature pressure relief valve is meant to dispense water when the pressure gets too high. It can cause problems when the water temperature is set too high. Check the water pressure and lower the temperature setting. Inspect the valve to see whether it is broken. It might need to be replaced.
Other problems that can cause a hot water heater to break include issues with the heating element gasket, vent obstructions, a loose drain valve or problems with the thermocouple or thermostat. A professional most likely will be needed to correct these issues.