by Francis Jock

Created on: September 21, 2008   Last Updated: April 27, 2012

One day you're enjoying life at home, the sun is shining, and all is well. Then you discover a puddle of water on the floor beneath your hot water heater. Alarm bells begin to ring in your head. Something is definitely wrong with your hot water heater's overflow pipe. How expensive is this repair going to be? The T&P valve has just ruined your day, and you didn't even know that such a thing even existed.

Take a look at your hot water heater. On the top or on the side of it you should find three connections. There will be a cold-water inlet line, a hot water outlet line and then a third line attached to a valve-thingy. That's the T&P valve, the source of your water leak, but probably not your problem. Why? Because it's supposed to leak, that is when it's working properly.

A T&P valve is a Temperature and Pressure valve. It is a safety device installed to protect you and your property from an explosion if the water heater's thermostat should fail and cause super-heated water to burst forth. They are mounted on either the top or the side of the water heater and should have a short discharge pipe pointing towards the floor. Some discharge pipes are connected into a drain line in the floor. These are not overflow pipes, as they only allow water to pass through when there is a problem.

These valves are not adjustable, and are designed to open and release the tank's water if it reaches a set temperature and/or pressure. You may find a tag attached to your heater's valve that will inform you how it operates. It is likely to be set to open at a temperature of 210 degrees F or a pressure of 150 PSI.

The message here is that the T&P valve is sensing that the water temperature and internal pressure is reaching an unsafe level. By opening a little, it relieves the pressure and thereby prevents the tank from possibly exploding. That's a good thing. The bad thing is that you have to pay attention to it and get it fixed. That means calling a plumber.

The T&P valve should be checked at least once a year. This is a simple process, although you are exposed to hot water unless you observe precautions. You can check the valve by lifting the small lever attached to it. This will open the valve enough to allow hot water to flow through the discharge pipe. Release the lever and the valve should close, stopping the flow. This is an easy way to test the valve and you can forget about it until next year, or until you discover that nasty puddle.

Unless tested at least once a year, T&P valves may become corroded and fail to operate properly due to presence of certain chemicals in the water. If you think that you have a problem, you should call a plumber. Only a qualified technician or a licensed plumber should replace a suspect T&P valve. Finally, you should be careful to follow the manufacturer's instructions and the tag attached to the valve.

With this bit of advice, you should know what to do when water is coming out of your hot water heater discharge pipe.

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