If you have a hot water tank in your home, a properly installed TPR valve is an essential device that helps protect, and alert the occupants that a problem may be forthcoming.
During a home inspection a hot water tank is just one of the hundreds of items looked at, and when I get in front of a hot water tank I look for many things that may be a potential problem.
Today I am going to focus on just one of the safety items that should be on all hot water tanks.
It’s called a TPR valve, or Temperature Pressure Release valve. These valves are designed to 
automatically release water in the event that the pressure or temperature in the hot water tank exceeds safe levels.
If a TPR valve is missing or malfunctions, water within the system may become superheated (surpassing the boiling point) and a tank rupture is possible. When super heated water is exposed to the atmosphere, it will expand into steam almost instantly, and this process can propel a hot water tank like a rocket through multiple floors, causing personal injury and property damage.
While water heater explosions are rare, because they require a combination of unusual conditions and failure of the safety components, it has happened and the results are catastrophic.
Click Here to see what a hot water heater tank under extreme pressure is capable of doing.
So what am I looking for when I inspect the TPR valve?
A properly installed TPR valve should meet these requirements:
Be constructed of a plumbing material rated for hot water, typically CPVC, copper, or galvanized steel.
Be properly rated for the hot water tank
Installed so the sensing element is within 6 inches of the top of the water heater
Is same diameter, or larger, than the supply pipe serving the water heater. (Usually ¾”)
Be as short and as straight as possible, to avoid undue stress on the valve, and installed so that it drains by gravity (downward).
Not have a valve, T-fitting, or threaded end, to avoid any scenario that might result in a restriction or capping of the discharge piping
Not be trapped, since standing water may become contaminated and backflow into the drinking water.
The valve should be connected to a discharge pipe (also called a drain line) that runs down the length of the water heater tank to within 6inches of the floor, or to a waste receptor with an air gap, or to visible exterior location.
What you should look for as a Home Owner?
First off I’m going to say that a missing TPR valve is extremely rare, (I have yet to find one missing ) but if it is missing, somebody who didn’t know what they were doing has endangered the occupants safety and you should immediately contact a qualified plumber.
Assuming a TPR valve is present; confirm that the data plate located on valve complies with the water tank data plate, if the data plate is missing replace the valve. The most common rating for TPR valve is 210 degrees and 150 PSI. Which means that the valve should activate if the water temperature in the tank exceeds 210 degrees F or the pressure within the tank exceeds 150 PSI. (Pounds Square Inch)
Make sure a discharge pipe is connected and appropriately sized. The discharge pipe should NOT be smaller diameter than the threaded portion of the valve, it should NOT be threaded or capped at the discharge point , and it SHOULD terminate within 6 inches of the floor.
If your tank is missing a discharge pipe have one installed.A missing or improperly installed discharge pipe is one of the most notable problems I find while inspecting hot water tanks, and is a relatively inexpensive safety item to have installed.
If you notice that the TPR valve on the tank is slowly leaking it’s a good indication that the valve requires replacement. If the TPR valve ever ejects a powerful stream of hot water it is alerting you that a problem exists, and you should immediately shut off the water and contact a qualified plumber for repair.
Although most TPR valves rarely become activated, it is an essential safety component on domestic hot water heaters. Guidelines concerning these valves and their discharge pipes reflect real hazards that every homeowner should take seriously. If you are unsure if your hot water tank is installed properly and that all the safety devices are in place contact a qualified plumber to further investigate.
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