According to American Water Heaters, the most common problems that cause a water heater to stop producing hot water are a flipped reset switch, a malfunctioning element or thermostat or a loss of power to the hot water heater. Troubleshooting is recommended to determine whether a new hot water heater is needed.
Water Heater Rescue recommends checking the reset button and breaker controlling the hot water heater first. If the breaker switches to the off position often or the high limit button resets regularly, there is usually a more serious underlying problem that requires replacing the hot water heater with a new model. For instance, moisture inside the control panel where the high limit reset button is located is a sign that a new hot water heater is necessary for safety reasons.
Lowe's recommends replacing any hot water heater that is over 10 years old, has visible rust or stops and starts working with no apparent cause. Obvious leaks are also a sign that it is time for a new hot water heater. In some cases, only the heating elements or thermostat needs to be replaced. When hot water is present but isn't hot enough, turning the thermostat up or replacing the thermostat may be the solution needed. Replacing the heating elements can also improve issues with insufficient hot water levels.
The heating element can be tested using an ohm meter only if the homeowner is familiar with, and comfortable, working with electricity, according to Water Heater Rescue. A plumber can be helpful in determining whether a new hot water heater is necessary or if a replacement part is sufficient to resolve the issue.