There are two possibilities: The first is the obvious, you re using a great amount of water and the hot water heater is trying to keep up with that. The other, more probable, cause is your pressure relief valve is opened and is continuously letting hot water flow through the valve. That valve should always be closed during the normal operation of the hot water heater. The best solution is to replace the pressure valve with the same PSI rating as the one that you take off and add an expansion tank (which is currently required by code). This should be done by an experienced handyman or licensed plumber.