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TP
valve Discharge
pipe Code TP = Temperature and Pressure Water heater TP valve is a safety device that prevents water heater from exploding |
 'TP relief
valve provides
2 in 1 protection against
excessive pressure
and excessive
temperature in emergency conditions. Mechanical
spring-loaded TP valve is reliable and fully automatic protection for
hot water
storage tanks and heaters.' TP valve will automatically close when
emergency conditions are over.''Water heaters are pressure tested to 300 pounds per square inch (PSI) and have a working pressure of 150 PSI."  -
T&P valve will open when the pressure inside the tank
exceeds 150 PSI, allowing pressure to vent safely. -T&P valve thermostat will push the spring valve open and release large volumes of hot water if water temperature at top of tank reaches 210°F. Resource pdf -Typical TP valve from Watts has a steam rating of 105,000 BTU and will work for any heater with output that is less than 105,000 BTU. -"The T&P valve rating can only be achieved with a full sized discharge line." -TP valve will not prevent rupture of tank that has been compromised by rust, defective weld etc, or protect a tank that is not rated for water heating. -"T&P valve is a safety device and is not intended for continuous operation to relieve thermal expansion." Pressure issues from heating water
Heating water causes water to expand in volume. The hotter the water, the more expansion, and the higher the pressure.
When thermostat is set to 120°F, then there is less pressure than a tank that is heated to 140°F. \ However, even 120°F can easily cause pressure that exceeds safe working limit of 150 psi. Normally excess pressure is not a problem because it expands back out the cold water line and into the city's water main -or- into the pressure tank of water well ... where the pressure is absorbed and mitigated by the pressure controls that are required for the water supply. Heating water becomes a pressure problem when heated water is blocked from expanding back into cold water line, createing what is called a closed system. Resource: closed system. Blockage can be caused by a check valve, pressure reducing valve, shut off valve or other obstruction in the cold water line. Result: TP will drizzle out water whenever tank is heating. Typically a pressure problem caused by closed system is solved by installing correctly sized expansion tank. Resource: Read about expansion tank High pressure can also be caused by the city or municipal water supply, often resulting in 100+ psi that causes TP valve to release short spurts of water, especially when water heater is heating. Ideal water pressure is 40-60 psi. Use a pressure gauge on water heater drain valve and compare with outdoor spigot. Compare household pressure with nearby homes. Buy: pressure gauge According to water heater manufacturers, the maximum pressure for home is 80 psi. Why? Anything over 80 psi risks TP releasing water, and shortened life of plumbing installation. If pressure is over 80 psi, then a pressure reducing valve is installed, along with an expansion tank Resource: expansion tank Rural water wells have a pressure switch that can be dialed down to 40-60 psi using small wrench. Replace pressure switch if pressure cannot be controlled.Resource: TP leaking lots of hot water Temperature issues and water heater ECO Residential gas
water heater has an ECO (energy cut off or high limit). The ECO trips when water inside tank reaches 180-188°F,
sometimes
requiring gas valve replacement. More
recent versions of electronic gas valves generally come with reset
protocol when ECO trips. Resource Troubleshoot gas valve
Residential electric water heaters have a red reset button or ECO that is located on upper thermostat. The ECO trips at 170-180°F +/-5°, shutting down electric power to elements. With electric water heaters, no damage occurs to thermostat because of ECO trip. If the ECO malfunctions on either gas or electric heaters, or something else happens to cause runaway heating, the TP will release the high temperature water, saving integrity of heater and preventing steam explosion. ''If the temperature probe on the T&P of a residential water heater senses water temperatures of 210° F, the valve will stay open until the temperature probe cools." The probe is at top of heater ... but cold water enters the bottom of the tank ... so it may take quite a while for the probe to cool. Result: you will have a large volume of water discharging out the TP before the temperature probe cools. Because super heated hot water is dangerous and can cause considerable property damage, it is best to have adequate floor drain, or route TP overflow tube to outside, or into a drip pan that has a drain line leading to outdoor or to an open drain etc. In this instance, do not expect a small metal can to catch the full volume of overflow. Footnotes, misc information. -Commercial heaters are sometimes rated higher temperatures, with commercial thermostat range as high as 180°+. -Heating water inside a tank causes pressure that is contained by the steel tank. "Water will not boil under pressure until the temperature reaches approximately 297° F. The energy potential in the superheated water is called latent heat energy and will flash to steam when exposed to normal atmospheric pressure. This flash to steam (steam explosion) has the explosive potential of over two million foot-pounds of energy." -"The maximum outlet water temperature for any water heater is 210°F ( 98.5°C)." This includes residential heater, commercial heaters, booster heaters, boilers of all type etc. Resource: Designing energy efficient commercial systems .pdf |
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 Code:-TP valve cannot be installed so it points in upward position. Must be installed horizontal on top of tank, or aimed downward on side of tank. -TP valve must be installed so probe inserts directly into water heater tank. - Install TP in port located on top of water heater or side of water heater near top of tank. -TP cannot be installed in lower part of tank (hot water rises). The probe must be located within top 6" of tank. -If heater does not have enough ports, an extra-length TP valve can be installed straight down into a Tee that is inserted into Hot outlet, as long as TP probe reaches into tank, but does not exceed maximum 6" deep into tank. -Each valve has a 'steam rating' or BTU per hour: 'T&P Valve must have a rating label that shows it is capable of discharging more BTUs than the heater is capable of putting into the water.' -So if heater is rated 40,000 BTU per hour (check label on side of heater), then the TP valve must have a rating that shows it can expel more than 40,000 BTU. -''TP valve must be marked with a maximum set pressure not to exceed the marked hydrostatic working pressure of the water heater (150 psi = 1,035 kPa) and a discharge capacity not less than the water heater Btu/hr or kW input rate as shown on the water heater’s model rating plate.'' ANSI Z21.22- CSA 4.4 and ASME. ...'' T&P valves tested under ANSI Z21.22 with ratings as certified and listed by CSA. Resource .pdf 
-TP valve rating cannot exceed 150 psi F for residential water heater.-Household water pressure cannot exceed 80 psi (50 psi is best), or TP can begin leaking water. Buy: pressure gauge Buy Watts telltale Water Pressure Test Gauge, 276H300 Telltale pressure gauge is left in place for a day, and marks the highest pressure so user can tell if there are pressure spikes that are causing TP valve to leak water, or other possible problems Resources: Read about thermal expansion TP leaking lots of hot water -TP valve overflow tube must connect directly to TP valve and run down to at least 6 inches off floor. -Cannot terminate near or on electric wires or junction box. Released water cannot contact person or electrical parts. -Pipe must be approved for hot water distribution: copper, pex, galvanized, CPVC (cannot use garden hose or PVC etc). -Overflow tube must be same diameter as valve discharge connection. Do not downsize pipe into smaller pipe. -Overflow tube cannot have shut off valve installed, or any obstructive valve. -No restriction, reducer coupling or valve can be installed on overflow tube. -If water heater has condensate drain (found on tankless, power vent, heat pump, condensing etc), the condensate drain cannot be inserted into overflow tube ... the overflow tube cannot have any holes or tees or other intersections. -Do not cap off TP valve or obstruct overflow tube. -End of overflow tube cannot be threaded. Must be protected from freezing, and cannot be concealed from view. -Overflow tube must pitch downward at all points. If tube has horizontal run, then it must pitch downward. -Shall be installed so as to allow complete drainage of both the Temperature-Pressure Relief Valve and the discharge pipe. -Can have maximum 4 elbows and max 30 feet length. Over 30 feet (9.14 m), or more than four elbows can cause restriction and reduce discharge capacity of the valve. --- Some manuals specify maximum 15' length and 2 elbows -If water heater is sitting inside a drip pan, overflow tube cannot be lower than top edge of drip pan. -Tube must terminate 6" above open drain, not inserted into drain. TP valve can draw water back into water heater if overflow tube is under water. -Some water heaters, for example under counter water heater or hybrid water heater may be installed in location that does not have available floor drain. TP cannot be inserted into a drain line for sink or washing machine etc. The TP tube can terminate 6" above a metal can. Discharge should not cause potential water damage. Homes can suffer damage if thermostat fails and TP begins releasing hot water. -If overflow tube is terminated inside a pipe, the end of tube must be visible to observe if water is being released from tank, and there must be air gap to prevent drain water from being sucked into water heater. -It is always best to have a floor drain, or a catch pan with minimum 3/4" line to outdoors, or terminate the TP overflow outdoors as long as freezing temperatures will not cause ice formation and blockage. -End of overflow tube cannot be restricted, blocked or obstructed by belongings, structure, snow, ice, rising water, damaged end of pipe etc. -Using a Temperature and Pressures Relief Valve that was subject to flood water is not advisable. -If water heater is used to heat a secondary tank or storage tank, then that second tank must also have it's own properly sized and rated TP valve. -If installation has more than one water heater, each heater must have it's own TP valve and independent overflow tube. Overflow tubes from multiple tanks cannot be combined into one. -T&P valves should be inspected and tested on every service call. Twice a year recommended. ''Ensure that (1) no one is near the outlet tube, and (2) the discharge will not cause injury or damage.'' -If TP fails to reset and continues to release water, raise again slowly and see if it will reset. If not, then close cold water inlet, turn off gas or electric, let tank cool, drain down a few gallons of water, then replace TP with properly rated/sized new one. -"T&P valve is not intended for the constant relief of thermal expansion (drizzle). A properly-sized thermal-expansion tank must be installed on all closed systems to control thermal expansion." -TP valve is last line of safety for functioning water heater. First line is the thermostat ECO reset button for electric heaters, and for gas, the thermostat, ECO, TCO etc depending on heater. Resource: How to replace TP valve Closed system Buy TP valves: Replacement TP valves at Amazon Teflon tape at Amazon |
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| • Shall not be smaller in size than
the outlet pipe size of the valve, or have any reducing couplings or
other restrictions. • Shall not be plugged or blocked. • Shall not be exposed to freezing temperatures. • Shall be of material listed for hot water distribution. • Shall be installed so as to allow complete drainage of both the Temperature-Pressure Relief Valve and the discharge pipe. • Must terminate a maximum of six inches above a floor drain or external to the building. In cold climates, it is recommended that the discharge pipe be terminated at an adequate drain inside the building. • Shall not have any valve or other obstruction between the relief valve and the drain.\ • Shall be approved material shown below. PVC and other piping material is not approved. ☑ Copper ☑ CPVC ☑ Galvanized ☑ Pex |
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 Prevent
explosionIf thermostat fails, it can cause run-away heating inside tank. When water inside tank reaches boiling point, a steam explosion occurs. Water boils at 212°F – at sea level – unless contained under pressure. At 52 psi gauge pressure, water would not boil until it exceeded 300° F A steam explosion will occur if pressure on a rusted tank, or a weld ruptures. Water heater explosion causes massive damage. To prevent this, a TP valve or temperature-pressure-release valve is installed on each water heater Instead of explosion, the TP valve releases hot water and cold water automatically refills tank, causing temporary cooling The cycle of overheated water and TP release continues until water heater is repaired. If the tank can deliver more BTUs into the water than the TP rating, or if the TP overflow tube is not installed to code, then the pressure can build up and cause explosion. Installing properly sized and rated TP valve, and following installation code is critical for water heater safety Applies to all water heaters/ gas, electric, tankless, condensing, oil-fired, solar, hybrid etc.... ''Why is hot water over 212° F dangerous? The containment vessel or storage tank used to store the hot water causes the danger. The tank is under pressure - the normal working pressure caused by the cold water supply. As water is heated under pressure, the boiling point rises. For example, with a nominal incoming supply pressure of 50 PSI, water will not boil under pressure until the temperature reaches approximately 297° F. The energy potential in the super heated water is called latent heat energy and will flash to steam when exposed to normal atmospheric pressure. This flash to steam has the explosive potential of over two million foot-pounds of energy.'' Resources: Thermal expansion How to install electric water heater How to install gas water heater Leaking water heater Thermal expansion |
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 |
Overflow
Tube is required Released water cannot contact person. |
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Add
6 wraps teflon tape when installing or replacing TP valve
Temperature probe must be inside water heater Buy TP valves: Replacement TP valves at Amazon Teflon tape at Amazon |
| Symptom | Action | ||
| What to look for: |
Some TP valves drain directly into drain pipe. Turn off all taps and put ear against pipe to hear sound of escaping water. If TP valve is continuously running out hot water, tank will have less hot water. Resource: Leaking water heater |
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| Quick fix for leaking TP: |  Raise TP lever for 5 seconds. See if obstruction is flushed out Keep extra TP valve on hand when doing this in event the TP continues leaking  Caution:
Keep Feet away from hot water coming from discharge tube!Resource: Leaking water heater |
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| Do NOT cap off TP valve | Caution: Do not cap off TP valve or discharge tube. Do not plug or obstruct TP valve or discharge tube. Obstructing TP valve can lead to explosion of water heater tank. |
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| Steady flow of water from TP | Raise
TP lever to clear blockage. Then if problem continues: Replace TP shown in steps below If water is unusually hot, then thermostat is bad: Bad thermostat: Replace Gas thermostat Bad thermostat: Replace Electric thermostat Bad electric element: Test elements |
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| Weeping TP valve | Dribbling,
intermittent
weeping: Foreign material in seat valve: Open valve to clear problem. Replace TP valve/ steps show below. High pressure: Check pressure with gauge on drain valve as shown below. Install pressure reducing valve and expansion tank. Reduce tank temperature: How to adjust temperature Replace TP shown in steps below FYI: If pressure reducing valve is installed, it will produce closed system .... expansion tank required . Closed system: Water confined to a storage tank or piping system, when subjected to a temperature rise of 10°F (increasing from 75° to 85°), increases pressure from 50 psi to 250 psi. Normal system (not closed) without pressure reducing valves, check valves etc: Water expands approximately 2% in volume for a 100°F temperature rise (from 40°F to 140°F) ....40 gallon water heater, water being heated to its thermostat setting will end up expanding to about 40.53 gallons. |
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| Large volume hot water released sporadically | Bad
thermostat Malfunctioning thermostat is only cause High temperature limit is around 210 degrees F Resource: Electric: How to replace electric water heater thermostats Gas: How to replace water heater gas control valve thermostat Identify/ troubleshoot by type of gas control valve |
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| Leaking threads on TP valve | Reseal
threads with 6
wraps teflon tape Probably mean tank is rusting: inspect tank each 6 months Resource: Replace tank: How to install gas water heater Reduce pressure using pressure reducing valve. Read more below Turn down thermostat temperature: How to adjust temperature Replace anode rod to prevent rusting: Replace anode |
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| Leaking weld around TP valve | Tank
rusted beyond repair:
Replace tank Resource: Leaking water heater How to install gas water heater |
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| Closed system/ high water pressure pressure | Install
pressure reducing
valve and expansion tank (read more lower on page) Resources Read about expansion tanks Read about expansion tanks and closed system Expansion Tank Installation pdf |
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Discharge
pipe Code |
TP
overflow tube runs down to at least 6
inches of floor. Overflow tube must be same diameter as valve discharge connection. Do not downsize pipe into smaller pipe. Overflow tube can have maximum 4 elbows and 30 feet length. End of overflow tube cannot be threaded. Tube cannot be lower than top edge of drip pan. Tube must terminate 6" above open drain. TP valve can draw water back into water heater if overflow tube is under water. Do not cap off TP valve or obstruct overflow tube Overflow tube cannot have shut off valve installed, or any obstructive valve TP valve is first line of safety for water heater. TP valve releases water when pressure or temperature is too high, and prevents possible water heater explosion |
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Reasons
TP
valve releases water: |
1)
Tank is overheating. Action: Open hot tap, and check for
overheated water. Adjust water heater temperature. How to adjust temperature
Bad gas control valve thermostat 2) Bad TP valve. Action: replace TP valve. Open TP valve once per year to test and dislodge obstruction. Clean sediment out of tank. How to clean sediment 3) Factory Heat trap nipples or inserts clogged. Action: remove heat traps Read more 4) Closed system caused by check valve, resulting in frequent TP replacement or constant drizzle. Action: remove check valve or install pressure reducing valve. Install expansion tank. Read more about closed system and expansion tank 5) High pressure. Action: put pressure gauge on water heater drain valve. Anything over 80 psi can damage tank. Install pressure reducing valve. Read more |
 Standard 3/4" pipe thread  Wind 6 wraps teflon tape on new valve. Most new valves already have Teflon tape on threads Buy TP valves: Replacement TP valves at Amazon 1/2" TP valve at Amazon Teflon tape at Amazon |
Step-by-step:
How
to
replace TP valve: 1) Turn off water. 2) Open tub spout to release pressure 3) Turn off power to heater Electric heater: turn OFF circuit breaker Typical Gas heater: rotate knob to vacation setting, or move knob to pilot position 4) Open bathtub tub spout on Hot side to release pressure 5) Let water cool Caution:
Make sure tank
has cooled before removing TP valve5) Open TP valve to lower water level. Or use drain valve on bottom of tank Resource: If water heater won't drain  6) Unscrew TP valve counterclockwise using 12-14" pipe wrench. 7) Install new valve and make sure threads have white teflon tape. Teflon tape will seal threads against leak. 8) Connect overflow tube that was attached to old TP valve. 9) Refill tank with water. Caution:
Do not turn water heater ON unless tank is full of water or it
can damage tank Wait for water to come out of bathtub spout in full stream before turning on water heater. When bathtub spout is running, then tank is full. Turn off tub spout. 10) Open new TP valve for a moment to let last bit of air out of tank. 11) Turn on water heater. Electric: turn on circuit breaker Gas: Rotate knob to previous temperature setting Resource: How to adjust temperature on water heater |
 Use 6 wraps teflon tape ☑ White for water lines ☑ Yellow for gas lines Buy Teflon tape at Amazon |
 Buy: Pipe wrench at Amazon Channel locks Resource: How to remove rusted element |
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 Inspect anode each 2-5 years Buy: Anode rods at Amazon Resources: Replace anode rod How to maintain water heater |
 Pressure reducing valve Pressure over 80 psi can damage water heater and household plumbing Buy Pressure reducing valve Resources Identify water heater valves Troubleshoot water pressure |
 Pressure gauge/ attach to water heater drain valve Pressure over 80 psi can damage water heater and household plumbing Buy Water pressure gauge Temperature-pressure gauge Resources Identify water heater valves Troubleshoot water pressure |
 Prevent flood Automatic water shut off valve Buy: Water detectors at Amazon Automatic water heater leak shut off at Amazon Resources: Leaking water heater/ steps |
 Water heater circulation system Buy: Grundfos at Amazon Resource: How to install recirculation system |
 Sharkbite pressure gauge Buy: Sharkbite pressure gauge Resource: Water heater valves |
 HOT side Sharkbite flexible water heater connector Buy: Sharkbite water heater connection Braided water heater line Stainless steel flexible connection Resources: How to install electric water heater How to install gas water heater Leaking water heater |
 COLD side Sharkbite flexible water heater connector Buy: Sharkbite water heater connection Braided water heater line Stainless steel flexible connection Resources: How to install electric water heater How to install gas water heater Leaking water heater |
 Buy: Impact wrench at Amazon Resources: Replace anode rod How to remove short water heater nipple |
  Gas water heater thermostats If tank is overheating or not heating correctly, replace thermostat Symptoms: Cold water, uneven temperatures, TP releasing water Buy Gas water heater thermostats at Amazon Resources: How to replace gas water heater thermostat Add another thermostat to water heater Troubleshoot gas water heater |
 Electric water heater thermostats Thermostats stick, melt and come out of calibration... replace thermostat Symptoms: Cold water, uneven temperatures, reset tripping, TP releasing water Buy: Water heater thermostats at Amazon Resources How to replace electric water heater thermostat Add another thermostat to water heater How to wire thermostats Marathon water heater thermostats Two water heaters Troubleshoot electric water heater |
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