As a home inspector I get to see a lot of homes every year and that means I get to see how many people actually do important home maintenance tasks such as caulking their windows and changing their furnace filter. One of the most widely neglected home maintenance tasks may be checking and testing your temperature and pressure relief valve on your water heater. Unfortunately I don't know of a more important home maintenance task than testing and inspecting this important safety device.
What is a Temperature and Pressure Relief Valve?
A temperature and pressure (T&P) relief valve is a safety device on your water heater which allows the tank to discharge if a set temperature or pressure rating is reached. It is installed to prevent the water heater from over pressurizing due to a malfunction in the tank. The device is installed on the top of side of the tank and should have a discharge tube running down to within 6 inches of the floor.
Why is a T&P valve important?
Without a T&P valve or with a damaged T&P valve the water heater could pressurize to the point that it actually explodes. This is a very dangerous situation as the pressure in a tank can be devastating. This happens because the water heats to the point it turns to steam and steam, unlike water, can become compressed. As more water turns to steam and the pressure of the compressed steam begins to build it has nowhere to go and it breaks the tank creating an explosion. Some 52 gallon residential tanks have the potential to explode with the force of two pounds of dynamite! This is enough force to send the tank hurtling through two floors of your home and out the roof.
What to do?
First and foremost, manufacturers instructions should always be followed exactly when testing or services a T&P valve, please consult all manufacturer literature before operating, testing, or servicing your T&P valve.
Most T&P valve manufacturers recommend testing your valve once a year by pulling up on the testing lever on the valve itself. This helps to keep the valve free of certain naturally occurring mineral deposits that may adhere to the valve, blocking waterways and rendering it inoperative. Before testing be sure a discharge tube is present and discharges to within 6" of the floor or another approved discharge location. Be aware that hot water will discharge from the tube once it is operated so stand clear of the discharge pipe. If water doesn't flow freely from the valve when operated it needs to be replaced immediately. Turn your water heater off and call a plumber.
T&P manufacturers also recommend an inspection of your T&P device every 2 to 4 years depending on local water conditions by a licensed plumber. They will look for signs of corrosion and defects that many homeowners may miss in their yearly checks. As a home inspector I recommend an annual check of the water heater by a licensed plumber who can also perform maintenance on the unit including cleaning the burners, flushing the tank, and evaluating the draft of the unit.