The answer to 'why is my water heater overflowing' is that the pressure relief valve on the water heater is likely malfunctioning or the tank has become overpressurized. This can happen due to a variety of reasons, such as a faulty thermostat, sediment buildup, or a problem with the pressure regulator.
When the pressure inside the tank gets too high, the relief valve opens to release excess pressure and prevent the tank from bursting. However, if the valve is stuck or not working properly, it can cause water to continuously overflow from the valve. This is a serious issue that requires prompt attention to avoid water damage and potential safety hazards.