A T & P valve on a water heater is a safety device to prevent a water heater from exploding. T & P is simply the abbreviation for temperature and pressure, but this abbreviation can be confusing when you think about how it applies to water heaters.
The reason to have a T & P valve is to monitor the pressure and the temperature on your water tank. This is an important device to have because it will prevent your water tank from exploding if there is a situation where the temperature of your water tank exceeds 180 degrees Fahrenheit, or the water pressure in you tank exceeds one hundred and fifty pounds. As a regular home consumer this kind of engineering may not make sense, but a T & P pressure valve is a very important feature on your water heater.
These T & P pressure valves are required to be installed on all water heaters in the Peninsula and Bay area, and should be checked every year for safety. This is because a properly installed and working T & P valve will prevent a possible explosion in your home water heater. While you may be able to reset the temperature device by pressing a small red button on your water heater, these kinds of thermostatically controlled devices are not replaceable on your own. Talking to a local plumber is the best way to clarify the need for these types of devices and why they are so important for home safety.