water heater

How To Incorrectly Install the Temperature Pressure Relief Valve - Or Boom Waiting to Happen

With any luck, when I do a home inspection, I get to stay nice and bored. That doesn’t happen as often as I would like unfortunately. Part of the boredom should come from verifying mundane details that nobody would ever get wrong.

Ha. Just kidding.

In this case, the mundane detail is the temperature pressure relief valve. These devices have been required equipment since the 1960s. Their purpose is to act as the last fail-safe on the water heater tank. The tank is a welded steel enclosure which means that it doesn’t structurally fail easily. It takes a considerable amount of energy to force it into failure. Or time, but that is more for leaks. Here I am concerned with a sudden catastrophic failure.

Most people would pay more attention to their water heater if they knew they were living with a bomb. Think I’m joking? Go check out this video from Mythbusters. Don’t worry, I’ll wait.

Welcome back! Impressive, wasn’t it.

Please note that they deliberately disabled the TPR safety to get the tank to go boom. In my job, I don’t need to assume intentional action or malice. Ascribing mistakes to simple silliness or ineptitude works just as well.

In the video below, a TPR vale is installed. Sadly, it is not installed correctly and has created the potential to turn the water heater into a house killer. Maybe a people killer, too. Bad news, that. It is, however, easily fixable.

The hottest water temperature I’ve ever check was 189 degrees on an old National Steel water heater from the fifties with no TPR valve. I practically begged the client to replace it.

Testing Water Temperature during the Home Inspection

As part of my home inspections, I test the water temperature at a minimum of one fixture, and sometimes, more. The State of Washington Standards of Practice states that the Inspector will report "Whether or not the water temperature was tested and state that the generally accepted safe water temperature is one hundred twenty degrees Fahrenheit."

Most inspectors simply report the generally safe accepted level and let it go. I don't for reasons that I'll cover here in a moment. First, the following will give you a sense for how hot water can injury. Note that these are for average adults, not small children or the very elderly.

  • Water at 100 degF or below is unlikely to scald an adult occupant at any exposure time.
  • Water at 120 degF for 5 minutes can cause 2nd & 3rd degree burns on adult skin
  • Water at 130 degF for 30 seconds can cause 2nd & 3rd degree burns on adult skin
  • Water at 140 degF for 5 seconds can cause 2nd & 3rd degree burns on adult skin
  • Water at 150 degF for 1.5 seconds can cause 2nd & 3rd degree burns on adult skin
  • Water at 160 degF for .5 seconds can cause 2nd & 3rd degree burns on adult skin

My record for water temperatures, actually measured in a home in Moscow, was 179 degF, hot enough to make coffee with. 150 degF is not all that unusual.

The reason all this came to mind is a report of Legionnaire's Disease in the Bronx. For those unfamiliar with the disease, it is bacterial in nature and a particularly nasty form of pneumonia. It is water-borne but, to infect, it needs to be inhaled.  Think humidifiers or showers where the bacteria in the water is atomized to particles that can be breathed.

The types of systems most likely to create ideal conditions? Cribbing from OSHA, "Warm, stagnant water provides ideal conditions for growth. At temperatures between 20°C-50°C (68°-122°F) the organism can multiply. Temperatures of 32°C-40°C (90°-105°F) are ideal for growth. Rust (iron), scale, and the presence of other microorganisms can also promote the growth of LDB."

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Sounds a lot like the well water we have here, conveniently heated to nearly ideal conditions for growth inside our water heaters.

Per OSHA, "Maintain domestic water heaters at 60°C (140°F). The temperature of the water should be 50°C (122°F) or higher at the faucet."

That's why I test the temperature and why, if the client is attending the inspection, we discuss the temperature. I don't call out high water temps as a safety hazard until I measure 130 degF. Even then, the discussion starts first with a question about who will be living in the home with the client.

I explain the state standard, which is based on manufacturer liability standards, as well as energy conservation standards. Then I explain the third leg of the risk triangle, bacteria control.

The reason that I might consider testing at more than one location in the home is that the newer faucets, especially for tubs and showers, have tempering valves. That is, the valve blends cold into the hot to moderate the temperature to safer levels. The place to get the most accurate reading on the output temperature of the water heater is usually at the utility sink since the hot and cold water controls separate.

If I get a low reading but a very fast rise on the temperature, I look for additional test points to confirm my reading. I don't want to inform the client that the temperature is under 120 degF if the test point is subject to tempering.

Depending on their particular circumstances, the clients may wish to leave the water temperature at a higher level than the standard. The point is to ensure that they are well informed on both the pros and cons of setting the water temperature for the home.

Get Rid of That 'Rotten Egg Smell'

 That rotten egg smell you get every time you turn on the hot water? You can get rid of it.

Both Pullman and Moscow have neighborhoods that have a lot of bacteria in the water supplies. That doesn't mean that it is always a health hazard - often it just really annoying. We have iron and sulfur bacteria in our area, courtesy of the aquifers that we have. Neither type of bacteria is particularly harmful, at least not at the levels usually seen. 

Here are some valuable tips on how to avoid or treat sulfur bacteria infestations.

Sulfur-reducing bacteria live in oxygen-deficient environments. They break down sulfur compounds, producing hydrogen sulfide gas in the process. Hydrogen sulfide gas is what gives the water that rotten egg smell. It's also highly corrosive. The sulfur smell may only be noticeable when the water hasn't been run for several hours which is why is seems to happen in vacant houses more often than occupied listings.

Why is it only in the hot water?

Actually, it isn't - it's in the cold water, too. The water heater  provides a good environment for Sulfur-reducing bacteria because it contains a "sacrificial anode." This anode is a magnesium rod that helps protect the water heater by corroding instead of the tank lining. SRBs are nourished by electrons released from the anode as it corrodes.

Water heaters infested with Sulfur-reducing bacteria can be treated.

The bacteria dies at temperatures of 140 degrees Fahrenheit or above, which is roughly equivalent to the high setting on most home water heaters that are in good working order. Setting the water heater on "high" will raise the water temperature to approximately 160 degrees Fahrenheit and kill any SRBs in the tank.

(This should only be done if the water tank has a pressure relief valve, and everyone in the house should be warned to prevent scaldings.) After about eight hours, the tank can be drained and the temperature setting returned to normal.

Raising the water heater temperature will solve the odor problem, but it may be temporary depending on the condition of the house plumbing supplies.

Removing the sacrificial anode will eliminate the problem, but it can also shorten the water heater lifespan significantly and likely will void the warranty. Replacing the magnesium rod with one made of zinc won't totally eliminate SRBs, but it will greatly reduce their numbers. Consult with a plumber before attempting to modify your water heater.

I'm selling my house - Should I fix this?

If you have your home listed for sale, I can absolutely guarantee you that this will improve the way your home appears to prospective buyers. I've had more clients than I can count wrinkle their noses at the rotten egg smell coming from the kitchen or bathroom when I am testing the functional flows. It doesn't help you sell your house.

Clean air and water evoke powerful, positive feelings. I strongly recommend that you fix that rotten egg smell.


Copyright © 2013 Paul Duffau