A recent, and ongoing, discussion with another home inspector here at Active Rain about water heaters reminded me that I have a picture of a temperature and pressure relief (TPR) drain pipe terminating in a small jar (Figure 1).

  Figure 1.

What happens with the TPR valve (yellow arrow in Figure 2) and the TPR drain pipe (red arrows in
Figure 2) at the water heaters is that if the water pressure or the water temperature inside the water heater gets too high, the TPR valve opens to let hot water under high pressure exit the water heater. That action lowers the water pressure and the temperature, returning things to a safer condition.

  Figure 2.

Generally, the drain pipe should be kept as short as possible with the termination 6-12 inches above ground level.

1. the water pressure in the water heater is or was too high,
2. the temperature of the water in the water heater is or was too high, or
3. the TPR valve is defective.

All three of those are dangerous conditions and can result in a water heater exploding. We've had a couple of water heater explosions here in San Diego since 2001. I went out and looked at the results of one where the 2,500-SF, 2-story home had been reduced to a 1,500-SF, 1 story home, and they found the water heater a half mile away on top of two cars in a strip mall parking lot. This video shows the result of a recent water heater explosion in a house in Phoenix.

Many jurisdictions allow the TPR drain pipe to terminate outside, but I think that's a dangerous location for several reasons:

1. Bugs can build nests in the pipe, or small critters can crawl up in the pipe, and clog it. My readers know that I love bugs and critters, so I want their homes to be safe as well, and this ain't it if a blast of hot water comes out of that thing!
2. If the TPR valve operates, you need to know about it. The only way you'll know is if you see the water. If the termination is outside, any water that has drained can soak into the ground or evaporate into the air before you ever see it. Not good.
3. Professionals from other industries might not know what that little pipe is and block it with their work. A great example is shown in Figure 3 where the concrete professionals installed a sidewalk too high, blocking the TPR drain pipe. I've also seen the stucco guys come along and stucco right over it "since it's not connected to anything out here."

   Figure 3.

I advise my Clients to have the TPR drain pipe terminate at the bottom of the water heater and then place a 5-gallon metal pail under the termination. Each time they walk by the water heater, look in the metal pail to see if there is any water. If there is, and the kids haven't been having water balloon fights, or you can't justify the presence of water any other way, call a plumber to check it out. Better to be safe than sorry.

In the two times that the TPR valve has opened on water heaters in my properties, both of them released only a few gallons of water, which is why I recommend that 5-gallon pail. It doesn't take much water and pressure release to lower the water pressure and temperature. Of course, if it opens regularly, such as during the week you're on vacation, you could come back to find half of your house gone or lots of water damage, so remember to turn the water heater thermostat to the low or vacation setting if you leave for more than a weekend.

In fact, it would be safest if you turned the thermostat down if you're gone for more than 24 hours. When I was young, whenever we went away for the weekend, we always unplugged the TV (so that a good ol' afternoon lightning storm wouldn't send a nice bolt through the television) and turned off the water heater and water.

I know that many home inspectors claim to find leaking TPR valves all the time, but it's been my experience that the only leaking valves are the ones that the home inspector has tested. I don't operate valves during an inspection because those that don't get used regularly (your outside hose bib gets used regularly) often fail when they are used. Since I'm not a licensed plumber, I can't make plumbing repairs, and except for my TECH inspections, I don't have a licensed plumber with me at the inspection. Additionally, I do a lot of inspections outside of plumbers' business hours, so if I cause a plumbing problem and have to call a plumber for an emergency, I'm going to be charged double-time after-hours rates. No thank you.

So while the termination and jar in Figure 1 might have the theory right, the termination is still too low to the ground (it should be 6-12 inches high) and the small jar is too small to hold a few gallons of water.

San Diego Gas & Electric and licensed plumbers recommend that all gas valves and water valves be tested annually, so if it cannot be proved (and it never can in homes being sold) that all the valves have been tested within the last 12 months, it's time for the seller to do it now if he wants to provide a safe home for the seller to move into.