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Pelletier's Home Inspection

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TPR Valve DHW Heater

Water Is Coming Out of the Tube on the Side of My Water Heater
or
My Water Heater Pressure Relief Valve Is Releasing Water

 

The name is Temperature Pressure Relief Valve (TPR valve).  This safety valve releases water (and thus relieves pressure) if either the temperature or pressure in the tank gets too high.  These valves are very important.  Water heaters can become bombs if the pressure gets too high and these valves fail to work.  See this major explosion caused by a small (5 gallon) water heater or this one when the TPR valve didn't work..

These valves can begin to run water either because 

  • the valve has become defective, or 
  • the pressure in the tank it exceeding the relief point.

May Be a Defective Valve

If your TPR valve suddenly started leaking when it didn't use to, and you haven't had any plumbing renovation work done recently, this is the most likely cause.  As the valves get older they sometimes begin to leak  I'm not sure why this happens.  I've heard people say they weaken over time, but I don't understand why that would be.  It may be if it has released small amounts of water over time this water has built up deposits in the valve that begin to interfere with it closing.  Or, perhaps a particle from the tank gets stuck in the seat holding it partly open.  There's a lever on the valve that lets you open it deliberately.  Some advise you do this periodically to be sure it's working properly.  In my experience if you open an older valve it's likely it will never close properly again -- it will begin weeping when it wasn't before.  As Terry Kennedy writes on alt.home.repair:  

It's not uncommon for older valves to get stuck in the open position when tested for the first time after many years - so be sure to know where the water shutoff valve for the inlet to the heater is.  A phone number of a plumber is a good thing to have handy.  And don't test it at 10 PM on a Saturday night. :-)  

These valves are cheap and there's only one problem replacing them -- sometimes they're hard to unscrew.  You may need a long handled wrench with a cheater.  Turn off the gas or electricity and cold water supply to the tank.  You only need to drain enough water to get below the level of the valve.  Don't drain a lot of water until you've broken the valve loose, so the weight of the water helps keep the heater from moving while you pull on the wrench.  

Wrap some teflon tape on the threads of the  new valve when you replace it.  

Note:  If you also replace the discharge tube, it must be made of a material that's rated for both high temperature and pressure.  This includes most rigid wall copper, iron and, in most places, chlorinated polyvinylchloride (CPVC plastic not regular PVC) pipe.  The pipe size must match the opening size of the TPR valve discharge (usually ¾ inch).  It must terminate 6"-12" above the floor, and the end cannot be threaded or have a fitting which permits connecting a plug or cap.  

May Be High Tank Pressure

The other reason for the TPR valve to run water is high pressure in the water heater tank.  This is usually caused by one of two things -- high main water pressure (water district or well) or a back flow prevention/check valve.

Backflow Valves

Houses built or renovated in the past 10-20 years may have a back flow prevention valve in the water supply line.  These valves only allow water to go in one direction.  Building codes have begun to require them so that once water enters your house it cannot move backward into the water supply system.  This introduces a new problem.  When the water in the water heater tank is heated it expands, making a greater volume of water.  This extra water needs somewhere to go.  If all the faucets in the house are closed it can't go that way.  Before these one way valves, water was simply pushed back out of the house into the main supply.  The backflow valve prevents this, so the extra water has no place to go and pressure builds in the tank until it exceeds the TPR valve set point (about 120 psi) and water comes out the TPR discharge tube.  As you may have guessed this isn't good.  

The solution is to install an expansion tank in the cold water line between the backflow valve and the water heater.  These tanks give the extra water a place to go.  If your builder installed a backflow valve he should have also installed an expansion tank but . . .    If you have an expansion tank it may have failed.

Main Pressure May Be Too High

If the main water supply pressure is too high this can also cause the the pressure to exceed the TPR valve set point.  The Uniform Plumbing Code calls for water to be delivered to homes for domestic use at between 50 to 70 psi.  Supply lines as well as appliances are designed to withstand up to 80 pounds per square inch.

Water pressure regulators reduce the pressure delivered by the water district to between 50 and 70 psi.  Over time the rubber and metal parts in these regulators can fail. When the regulator fails, water pressure to the home increases putting a strain on valves, hoses and appliances they were not designed to withstand.  A solution to the problem its to install your own pressure regulator on your incoming water line.  But, this pressure regulator will also behave like a backflow valve -- it will not allow water to go backward through it -- so you'll also need an expansion tank if you install your own pressure regulator.

If you suspect the pressure in your water heater is too high you can buy a water pressure gauge for about $9 (one place is Home Depot) and check it.

Connect the gauge to the water heater drain faucet (garden hose thread).  Run a hot water faucet until the water heater begins heating.  Close the faucet.  If the pressure starts creeping up as the heater heats the water, there is a backflow valve or in-house regulator creating a closed system.

If the pressure does not increase as the water is heated, but the pressure reads above 80 psi all the time, your supply pressure is too high.  You should consider contacting the city/water district, and if they don't do something consider installing your own regulator.  To check the supply (main) pressure you can also connect the gauge to an outdoor faucet, and turn on the faucet. Make sure the faucet is "regulated". Some outdoor faucets are unregulated.  If the pipe connected to the faucet comes out of the wall it's probably regulated.

Temperature/Pressure
Relief (TPR) Valves

Common code defects that may compromise the use and safety of your plumbing system.

   
Uncover the most common code violations our Guardian Inspectors encounter in the field.  Learn what to look for and why.

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The Temperature/Pressure Relief Valve

One of the most common code violations our inspectors observe in the field involves the Temperature/Pressure Relief (TPR) Valve on the water heater unit.  The purpose of this article is to assist property owners and inspection professionals in identifying these common code violations so they may be prevented and corrected.

What is a Temperature/Pressure Relief Valve?

Section 3303.1 of the International One- and Two-Family Dwelling Code[i] requires the installation of a combination Temperature/Pressure Relief Valve (commonly referred to as a TPR valve) or a separate temperature relief valve and a pressure relief valve on every water heater. The purpose of the TPR valve is to provide an important safety mechanism that allows for the immediate discharge of excess temperature and pressure that builds up inside the tank as the water is heated. 
  
If not allowed to properly discharge, this excess temperature and pressure will eventually cause the tank to explode.  One such tragedy occurred in Spencer, Oklahoma at the Starr Elementary School on January 9, 1982 where six children and a teacher were killed when the school’s water heater exploded with the force and effect of two pounds of dynamite.  This occurred due to a malfunctioning TPR valve.  Figure 1 (right) shows a typical Temperature/Pressure Relief (TPR) Valve installation on a gas water heater.

Figure 1 - Typical installation of a Temperature/Pressure Relief (TPR) Valve on a gas water heater
 
Consequently, Code Section 3303.3[i] dictates that a TPR valve must discharge once the pressure inside the tank reaches 150 psi (pounds per square inch).  Code Section 3303.4[ii] specifies that the TPR valve must be installed within the top 6 inches of the water heater tank in order to enable the valve to discharge at a temperature of no greater than 210°F.  As a result, any discharge piping must be rated to withstand at least 210°F to prevent melting and blockage of the TPR valve when discharged.
Common Violations in the Field

As we have seen, the presence of a functioning Temperature/Pressure Relief (TPR) Valve on a water heater is extremely important.  However, there are other factors to consider in ensuring the protection of property and people who may be standing near the water heater when the valve actually discharges.  Namely, where does the scalding water or steam go once the valve is allowed to discharge? 

The following are the more common discharge piping violations we observe in the field:

1)  Improperly-Sized Discharge Pipe

Code Section 3303.6.1.[i] requires that the TPR valve is fitted with a discharge pipe that provides the same size opening as the valve outlet itself.
 
Figure 2 (right) shows a TPR Valve that has been fitted with a discharge pipe that is smaller than the size of the valve outlet.  This is a common defect that is strictly prohibited because smaller discharge pipes restrict the flow of the pressurized water released by the valve. This creates a dangerous bottleneck, building-up even more pressure at the point of discharge that can cause the tank to explode.  Personal injury (or death) and property damage may result.

Figure 2 - Improperly sized TPR discharge pipe

2)  Missing Discharge Pipe

In many instances, the discharge pipe required in Section 3303.6.1.[i] was never installed at all.  This normally occurs during replacement or initial installation of the water heater.

Figure 3 (right), shows a missing TPR discharge pipe.  This creates a dangerous condition whereby the TPR valve will spray scalding steam or scalding hot water onto anyone (or anything) that happens to be near the water heater when discharge occurs. 

When you consider that the TPR valve discharges water at 210° F., serious injury or property damage will result.

Figure 3 - Missing TPR Valve discharge pipe
 
3)  Improper Termination of the Discharge Pipe
Ideally, the TPR valve discharge pipe will be vented to the outside of the building where the scalding water or steam can be discharged without posing a threat to people or property.   However, in many installations direct piping to the outside is not possible or is deemed to be too costly to provide.

Accordingly, Code Section 3303.6.1[i] does allow for the discharge pipe to terminate inside a receptacle (or spill pan) as long as an air gap is provided between the end of the discharge pipe and the top rim of the spill pan itself without creating a hazard or potential cause of damage.

This is clearly not the case in Figure 4 (right). Here we see the copper discharge pipe runs down the right hand side of the water heater tank to terminate into a metal spill pan below.  However, the problem lies in the fact that the end of this discharge pipe terminates below the upper rim of a shallow spill pan.

This installation of the discharge pipe poses several potential dangers. 

First, the discharge pipe may be able to siphon any liquid that may accumulate inside the pan. This is due to the fact that the end of the discharge pipe terminates below the top rim of the receptacle itself. Once siphoning occurs, the liquid (be it dirty water, household chemicals, oil, etc.) will be drawn back into the water heater tank, thereby contaminating the household drinking water supply.

Fig4_DischargeIntoPan.jpg (141264 bytes)

Figure 4 - Improper Termination of Discharge Pipe.

While this occurrence is admittedly unlikely due to the fact that the TPR valve would have to fail (stay open) while a simultaneous drop in line pressure would create a siphon, the mechanical potential does exist for this contamination to occur.  Thus the air gap provision in the building code.

Secondly, and even more likely, is the risk of personal injury when this TPR valve discharges.  This is because the discharge pipe terminates into a spill pan that cannot safely catch the flow of water or steam during discharge.  When you consider that the TPR valve discharges at 150 psi, which is five times greater than the force of your garden hose, the scalding water can strike the bottom of the shallow pan and spray out in all directions.

Therefore, a deeper spill pan receptacle with adequate circumference would be advisable over the shallower, tightly-fitting spill pans commonly observed in the field.

Figure 5 (right), shows a spill pan that tightly fits the base of a water heater. Unfortunately, such an installation accomplishes little in the way of catching water or steam from the TPR safety discharge valve, rendering the spill pan useless.

Spill pan installations depicted in this photograph are common in condominiums and some residential homes where space is a premium.

Fig5_SpillPan.jpg (249239 bytes)

Figure 5 - Inadequate Water Heater Spill Pan Sizing
 

Summary

As we have seen, the Temperature/Pressure Relief (TPR) Valve serves an extremely important function – ensuring the safe and proper operation of the water heater.  As professional home and commercial property inspectors, we frequently observe the code violations discussed in this article and encourage property owners and inspection professionals to take the time and effort to identify and correct them. 

Consequently, the conditions presented in this article should be corrected immediately by a qualified and licensed contractor.

illustration showing all of the parts of a gas water heater  

 

Gas water heaters are the most common type.  Gas gets the tank up to temperature about twice as fast as electrics do, and costs less than half what it takes for an electric unit.

The tank should be firmly affixed to a structure such as the wall in earthquake prone areas to prevent a potential gas fire if the tank falls over and breaks the gas connection.

TPR Valve

Storage type units that have a tank have a TPR valve (and so do electrics). Some times tankless units have TPR valves, and sometimes they don't. 

The TPR valve (Temperature Pressure Relief) also known as a T&P valve, pop-off valve,  or just relief valve, is a safety device on gas water heaters that releases pressure from the tank if the pressure or temperature reach unsafe levels. 

The TPR valve is usually mounted on the top of the tank, but can sometimes be mounted on the side of the tank.

A manual release lever located on the relief valve. According to most manufacturers elief valves should be periodically tested by lifting the manual release lever at least once a year.

Due to the scalding potential of the discharge from the T&P valve, the outlet from the valve should be piped to a safe area. Typically they are piped down to within 6 inches of the floor or even outside of the dwelling at near ground level.  Check with your local building department for local building code requirements related to the relief valve discharge plumbing.

Anode

The sacrificial anode is a metal rod usually magnesium or aluminum which helps prevent corrosion of the metal tank. Electrolysis eats away the metal anode instead of the metal of the tank. Once the anode is gone the tank itself begins to corrode.  To prolong the life of the tank, make sure your anode rod is still there, and replace it when needed.

The anode is screwed into the top of the tank and can be replaced.  Sometimes the anode is built into a special outlet fitting. Softeners can cause the anode to wear out more quickly.

Bacteria can react with magnesium anodes causing hydrogen sulfide which can cause a rotten egg odor. Switching to an aluminum anode rod can help eliminate the odor problems.

Dip Tube

The dip tube is a long narrow tube that directs incoming cold liquid to the bottom of the tank, preventing pre-mature mixing of incoming cold liquid with the out going hot liquid at the top of the tank.  Without the dip tube, or with a broken dip tube,  it may seem as though you run out very quickly, or you just get a luke warm temperature.

Thermostat

The thermostat senses when the tank drops below a certain pre-set temperature and causes the burner to come on.  When the desired temperature is reached, the thermostat shuts off the burner. There is a knob that allows you to set the temperature to warm med or hot.

Drain Valve

The drain valve allows the tank to be drained for various reasons including periodic removal of sediment or for replacement. In areas with high mineral content, it is recommended to drain at least 5 gallons from the drain valve every six months or so to prevent sediment build up.  

Avoid cheap plastic drain valves that can easily break off.  Replace plastic drain valves with a good metal ball valve.  Ball valves make it easier to drain the tank as well.

Water Is Coming Out of the Tube on the Side of My Water Heater
or
My Water Heater Pressure Relief Valve Is Releasing Water

 

The name is Temperature Pressure Relief Valve (TPR valve).  This safety valve releases water (and thus relieves pressure) if either the temperature or pressure in the tank gets too high.  These valves are very important.  Water heaters can become bombs if the pressure gets too high and these valves fail to work.  See this major explosion caused by a small (5 gallon) water heater or this one when the TPR valve didn't work..

These valves can begin to run water either because 

  • the valve has become defective, or 
  • the pressure in the tank it exceeding the relief point.

May Be a Defective Valve

If your TPR valve suddenly started leaking when it didn't use to, and you haven't had any plumbing renovation work done recently, this is the most likely cause.  As the valves get older they sometimes begin to leak  I'm not sure why this happens.  I've heard people say they weaken over time, but I don't understand why that would be.  It may be if it has released small amounts of water over time this water has built up deposits in the valve that begin to interfere with it closing.  Or, perhaps a particle from the tank gets stuck in the seat holding it partly open.  There's a lever on the valve that lets you open it deliberately.  Some advise you do this periodically to be sure it's working properly.  In my experience if you open an older valve it's likely it will never close properly again -- it will begin weeping when it wasn't before.  As Terry Kennedy writes on alt.home.repair:  

It's not uncommon for older valves to get stuck in the open position when tested for the first time after many years - so be sure to know where the water shutoff valve for the inlet to the heater is.  A phone number of a plumber is a good thing to have handy.  And don't test it at 10 PM on a Saturday night. :-)  

These valves are cheap and there's only one problem replacing them -- sometimes they're hard to unscrew.  You may need a long handled wrench with a cheater.  Turn off the gas or electricity and cold water supply to the tank.  You only need to drain enough water to get below the level of the valve.  Don't drain a lot of water until you've broken the valve loose, so the weight of the water helps keep the heater from moving while you pull on the wrench.  

Wrap some teflon tape on the threads of the  new valve when you replace it.  

Note:  If you also replace the discharge tube, it must be made of a material that's rated for both high temperature and pressure.  This includes most rigid wall copper, iron and, in most places, chlorinated polyvinylchloride (CPVC plastic not regular PVC) pipe.  The pipe size must match the opening size of the TPR valve discharge (usually ¾ inch).  It must terminate 6"-12" above the floor, and the end cannot be threaded or have a fitting which permits connecting a plug or cap.  

May Be High Tank Pressure

The other reason for the TPR valve to run water is high pressure in the water heater tank.  This is usually caused by one of two things -- high main water pressure (water district or well) or a back flow prevention/check valve.

Backflow Valves

Houses built or renovated in the past 10-20 years may have a back flow prevention valve in the water supply line.  These valves only allow water to go in one direction.  Building codes have begun to require them so that once water enters your house it cannot move backward into the water supply system.  This introduces a new problem.  When the water in the water heater tank is heated it expands, making a greater volume of water.  This extra water needs somewhere to go.  If all the faucets in the house are closed it can't go that way.  Before these one way valves, water was simply pushed back out of the house into the main supply.  The backflow valve prevents this, so the extra water has no place to go and pressure builds in the tank until it exceeds the TPR valve set point (about 120 psi) and water comes out the TPR discharge tube.  As you may have guessed this isn't good.  

The solution is to install an expansion tank in the cold water line between the backflow valve and the water heater.  These tanks give the extra water a place to go.  If your builder installed a backflow valve he should have also installed an expansion tank but . . .    If you have an expansion tank it may have failed.

Main Pressure May Be Too High

If the main water supply pressure is too high this can also cause the the pressure to exceed the TPR valve set point.  The Uniform Plumbing Code calls for water to be delivered to homes for domestic use at between 50 to 70 psi.  Supply lines as well as appliances are designed to withstand up to 80 pounds per square inch.

Water pressure regulators reduce the pressure delivered by the water district to between 50 and 70 psi.  Over time the rubber and metal parts in these regulators can fail. When the regulator fails, water pressure to the home increases putting a strain on valves, hoses and appliances they were not designed to withstand.  A solution to the problem its to install your own pressure regulator on your incoming water line.  But, this pressure regulator will also behave like a backflow valve -- it will not allow water to go backward through it -- so you'll also need an expansion tank if you install your own pressure regulator.

If you suspect the pressure in your water heater is too high you can buy a water pressure gauge for about $9 (one place is Home Depot) and check it.

Connect the gauge to the water heater drain faucet (garden hose thread).  Run a hot water faucet until the water heater begins heating.  Close the faucet.  If the pressure starts creeping up as the heater heats the water, there is a backflow valve or in-house regulator creating a closed system.

If the pressure does not increase as the water is heated, but the pressure reads above 80 psi all the time, your supply pressure is too high.  You should consider contacting the city/water district, and if they don't do something consider installing your own regulator.  To check the supply (main) pressure you can also connect the gauge to an outdoor faucet, and turn on the faucet. Make sure the faucet is "regulated". Some outdoor faucets are unregulated.  If the pipe connected to the faucet comes out of the wall it's probably regulated.


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