You may be running out of hot water for many reasons, such as: Your water heater is too small for your needs. You have low or fluctuating water pressure. Your tank is improperly insulated and loses heat through the sides. The heater elements are dirty and can't heat the water efficiently. You're using too much hot water at one time. The water heater vent is clogged. Your thermostat settings are wrong, or the thermostat is malfunctioning. You have other plumbing issues like old pipes or clogs. There is a leak somewhere in the system.