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Water Heater T & P Valve

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Issue 78, December 15, 2002

Personal Note: This weeks article was authored by my Dad, Rudy Hilton, who I often say has forgotten more than I know. Most in this town doesn't realize that at one time R. J. Reynolds had its own construction operation, which if compared, would have been ranked as one of the largest in the world. Dad was part of that operation, which not only involved construction, but also maintenance of all R.J.R facilities. Later in life he served as Director of the Physical Plant for Wingate & later Samford Universities.

Danger Zone


In my home, your home and in almost every home you list or sell is a device which, if it malfunctions, creates the explosive potential of nearly 200 sticks of dynamite, enough to destroy the home and kill all the occupants. It is part of most, if not all, of your sales. You didn't know you were in the business of marketing bombs, did you? Do you think you might want to read this one?

Do you know what is it?  

It is the tank type water heater. We can help prevent such disaster in our clients lives by helping them become aware of the needs of their water heater and especially its temperature and pressure relief (T&P) safety device.

The explosion of a tank type water heater can be caused by a malfunction which causes the heater to continue to heat even though the set point of the thermostat has been reached.Water heaters are designed to operate safely with a (T&P) valve to automatically release excessive pressure to prevent an explosion.Manufacturers instructions suggest at least an annual testing of this T&P valve to be sure it would function if such a malfunction were to occur.When was the last time you tested yours? (Note: Home inspectors do not test these valves because they often fail during the test requiring replacement.) In some hard-water areas, as many as one out of every four T&P valves fail this annual test. Such water heaters are a disaster awaiting only the malfunction of a thermostat to explode with devesting fury.

Water heaters are one of the most beneficial component of our homes providing hot water for baths, washing of clothes and dishes for their lifetime if properly cared for. If not cared for they can explode with destructive force comparable to the chaos we see on television caused by suicide bombers in some parts of the world.Why is it that you are concerned about the suicide bomber but pay no attention to the potential for such occurrence in your own home. Any home owner who fails to maintain the T&P valve properly may unknowingly and unwittingly become a suicide bomber in his or her own residence.

Why do we have so few explosions of water heaters?

Because of the simplicity, quality and reliability of a safety device know as the Temperature and Pressure Relief Valve (T&P Valve). Repeated inspection by installation and repair contractors, plumbing inspectors, building inspectors and home inspectors assure that most problems with the T&P valve are caught and corrected.(Note: This is the same type valve that protects heating system hot water boilers from explosion.) Water heating components usually malfunction in a safe manner and do not cause overheating. Therefore, home owners are able to have proper repair performed hopefully by a reputable and reliable plumbing repair contractor who knows what he or she is doing.  

What kind of damage has water heater explosions caused?

The Seattle Post-Intelligencer on July 28, 2001, reported on an electric water heater tank explosion where the pressures built up until the tank exploded. According to the article the force of the explosion blew the tank across six lanes of traffic and ended up in a parking lot more than 439 feet away.

In 1993, an older water heater exploded in a home in South St. Paul, Minn. The 200-pound tank shot through a floor, ceiling and roof like a missile to a height of 150 feet in the air. The explosion destroyed the home and injured two people. 

In 1982 six children and one teacher were killed when a hot water heater exploded in the Star Elementary School cafeteria in Oklahoma City. Regulations were later enacted there requiring annual inspection of domestic hot water heaters in all public facilities.

What does the Home Inspector observe for safe operation of the homes water heater?

That the water heater has a T&P valve installed and that it is piped and not obstructed so that any hot water or steam that may be released will not create a hazard to bystanders.The discharge pipe must be the same size as the discharge outlet and is normally piped to a few inches above the floor discharging down and observable. Note: In some instances, most noticeable in multi story multifamily homes, this discharge line may be piped to the exterior. 

The Home inspector is not responsible to: check the sizing of the T&P valve or to test its operation.  

Codes, including manufacturers recommendation and good practice call for: Proper sizing of the T&P valve. The T&P drain should never by plugged up or be connected into drain pipe or to any location which would prevent the visual observation of discharge.This is important because if the T&P valve leaks it indicates a problem is developing that should be corrected. Observation of discharge will sometimes show that sediment is becoming a problem. 

It is recommended that the T&P pipe discharge into a bucket so that the homeowner would be able to tell that the valve was discharging when no one was present to observe it and to evaluate any sediment. This will also prevent minor discharges from flooding the area near the heater.

Water Heater Maintenance

Since water heater explosions still occur, an essential safety measure no homeowner can afford to overlook is the annual testing (operation) of the T&P valve. It should be replaced if it fails to work.

Sediment should also be drained from the bottom drain of the tank at least annually, quarterly would be better if heavy sediment is encountered.Remember that sediment can block and prevent proper operation of the T&P valve. Draining a quart of water from the bottom of the hot water tank every three months removes sediment and boosts efficiency. It is safer if electricity is cut off when this is done.

Sediment is sometimes brought in with the incoming cold water.Another source of sediment is the sacrificial anode.This anode is designed to sacrifice itself by rusting and decomposing first and thereby protecting other elements of the tank.The oxidized material from the anode become debris in the tank. Because when the anode is fully sacrificed, oxidization of other components accelerates, replacement of the expended anode rod can increase the productive life of a heater.It should be checked periodically.

Dip tubes (the pipe which carries the cold incoming water to the bottom of the tank) are also sometimes a source of sediment. Also, broken dip tube may permit the incoming cold water to mix with the outgoing hot water at the top of the tank causing it to seem as though the water heater is running out of hot water. 

The California Department of Consumer Affairs is warning residents that this little-known device (the dip tube) in their home water heaters may be faulty, causing damage to heaters and plumbing. The water-heater dip tube is a long slender device which delivers cold water from the external water source to the bottom of the heater. Perfection Corp. of Madison, OH, manufacturer of virtually all dip tubes used in the United States, produced an unknown number of defective tubes between 1993 and 1996. These tubes can decompose, sending tiny particles of plastic and sludge through the plumbing system. This in turn can clog the faucet aerators and screens causing low water pressure at the fixtures. If plastic particles or excessive sludge is being caught on aerator screens through which a lot of hot water passes, the dip tube should be checked.  

Other Potential Water Heater Hazards

Fires Involving Gas Water Heaters

According to the Consumers Product Safety Commission, fires involving gas water heaters result in 316 injuries and 17 deaths in a typical year. A gas water heater can be located in a garage or utility room where it draws in combustion air near ground level. If a hydrocarbon such as gasoline or other flammable liquids which produces heavier-than-air vapor is spilled in the vicinity of the water heater, a fire or explosion is extremely likely.

When the area around a gas water heater is used for storage, the potential of a fire is greater. Storing flammable liquids and burnable objects, such a paper or cardboard boxes near or on top of the tank around the vent is especially dangerous.


While neither the Home Inspector, nor the Real Estate Agent is responsible to check the setting of the water heater thermostat temperature. I mention this subject because an average of one person, mostly children, receives a third degree burn each hour from excessively hot tap water, and you thought that it was only from hot coffee as fast food restaurants.

The US Consumer Product Safety Commission (CPSC) reports that each year, approximately 3,800 injuries and 34 deaths occur in the home due to scalding from excessively hot tap water. The majority of these accidents involve the elderly and children under the age of five. All users are encouraged to lower their water heaters to 120 degrees Fahrenheit. In addition to preventing accidents, this decrease in temperature will conserve energy and save money. A rule of thumb is that every 10-degree reduction in your water heater thermostat saves you 13% per year -- as much as $60.

Risk of serious scalding is greatest while bathing or showering. A small child doesn't have to soak in hot tap water to get scalded. Tragically, injury can happen literally in the blink of an eye. In 1/2 second a baby can suffer a severe third degree burns in 150 degree water!Or in 140 degree water scalds in just 1 second!But it takes four minutes for water at 120 degrees to scald. Small children, or the elderly, or the disabled are four to six times more susceptible to scalding an a healthy teenager or adult because their skin is thinner and more sensitive and their reactions slower. 

Most adults will suffer third-degree burns if exposed to 150 degree water for two seconds. Burns will also occur with a six-second exposure to 140 degree water or with a 30 second exposure to 130 degree water. 

Turning down the temperature on home hot water heaters is the law in the state of Washington which requires hot water heaters in new homes to be set to a lower and safer limit of 49 degrees Celsius, or 120 degrees Fahrenheit. And since that law was passed, it has led to a major drop in hot water burns. 

A potential danger exists when an undersized water heater is compensated for by increasing the temperature above 120 degrees Fahrenheit.Another grave danger is where small children or disabled individuals visit a home where higher tap water temperature is routinely used by healthy teenagers and adults and reasonable precautions are not made for the visitors.

How much does water heating cost?

An EREC Fact Sheet published by the U. S. Department of Energy states that the cost for heating water is generally one-seventh of the total utility cost.

The actual cost of hot water depends on the temperature of the incoming water, the efficiency of the heater, the setting of the thermostat and the amount used. Water heating costs usually goes up in the winter time when the incoming water is colder.

What can we do to protect our clients?

We can advise our clients of the potential hot water heater dangers from explosion and scalding.

Interesting antidote from Chris:

Dad sent this article to me on the 10th, on the 11th I received and e-mail from him containing this: 

"Yesterday morning Walter (Dad's brother) and I went to eat breakfast at a restaurant (location deleted to protect the guilty). They were unable to open because they had no water.I, being the helpful sort of person that we Hiltons are, agreed to look around and see if I could locate the problem -- it eventually turned out to be a frozen water main.In the course of looking I discovered that the T&P valve (on the water heater) had leaked on the floor, so the operator did the logical thing that an uninformed person would do, they installed a pipe plug in the escape port of the T&P valve.I told the lady now operating the restaurant that was a no-no and that a malfunction in the heater could cause a tremendous explosion.She apparently did not understand or take me seriously.I checked this morning and the plug is still in the T&P valve.It could make headlines anytime now. Hopefully they use enough hot water during the day that a boom would occur after hours.It needs to be corrected -- but how if the owner or operator does not assume the responsibility? Any suggestions?"

During Dad's research he found what appears to be a good web site for plumbing issues at ""

If you enjoyed and gained useful information from this article you can drop my Dad Rudy Hilton an e-mail at "" If you encourage him, he may write some more! Please send a copy to me at ""

Thought for the week

If I could only install a T&P valve on my wife and children.
You can bet they think the same about me.

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