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TECHNICAL SERVICE DEPARTMENT
Technical Service Bulletin
1-800-432-8373
Temperature And Pressure Relief Valves
Discharge of the T&P valve may indicate that an unsafe temperature or pressure condition exists.
Contact a licensed plumber immediately!
Temperature and Pressure Relief Valves, also called T&P valves,
are emergency safety limit devices that will prevent or relieve
overheated water and pressure. Without a relief valve during an unsafe
condition, the pressure inside the tank would rise to the point the tank
may rupture or explode. This would cause potential damage to both
people and property. Rheem water heaters are pressure tested to 300
pounds per square inch (PSI) and have a working pressure of 150 PSI.
The T&P valve is designed to open when the pressure inside the tank
exceeds 150 PSI, allowing pressure to vent safely. The T&P valve will
also open if the water temperature reaches 2100 F. The valve will remain
open allowing cold water into the tank until the unsafe condition is over.
Why is hot water over 212° F dangerous? The containment
vessel or storage tank used to store the hot water causes the danger. This
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 superheated 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.
The Temperature and Pressure Relief Valve is
the safety device that prevents these conditions from
happening. It is a 2-in-1 device that responds to both
pressure increases and temperature increases. When
actuating by pressure, the T&P valve will open and
allow the tanks internal pressure to drop below 150PSI.
Generally, when you see a T&P valve weeping or
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dribbling, it is due to pressure (thermal expansion) or foreign material such
as calcium buildup in the valve seat. This material on the valve seat will
prevent the valve from closing tightly. If the valve is discharging large
quantities of water, them the release is due to temperature. Recall the T&P
is installed in the top six inches of the tank. If the temperature probe on the
T&P senses water temperatures of 210° F, it will open the valve. The valve
will stay open until the temperature probe cools. With cold water entering
the bottom area of the tank, you can see a large volume of water (gallons)
will be discharged before the temperature probe cools.
Technical Competence, Product Confidence
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Page 2
TECHNICAL SERVICE DEPARTMENT
Technical Service Bulletin
1-800-432-8373
Temperature And Pressure Relief Valves
Discharge of the T&P valve may indicate that an unsafe temperature or pressure condition exists.
Contact a licensed plumber immediately!
T&P valves should be inspected and tested on every service call. When checking the
valve, also check the rating plate on the valve. Many changes may take place in a plumbing
system after the original installation. Through a systemic reinspection program, we can insure
that the safety device is working properly. The T&P Valve must be capable of discharging more
BTUs than the heater is capable of putting into the water.
Installation of a temperature and pressure relief valve is critical to the safe operation of a
water heater. The basic rule is that the T&P valve must be installed so that the temperaturesensing probe is immersed in the hottest water in the top six inches of the tank. All water heaters
manufactured by Rheem – Ruud have a separate and special connection designed for the T&P
valve.
T&P Location
Residential Electric
T&P Location
Commercial Gas
Here are some common T&P valve errors:
No T&P installed or pressure only relief valve
installed
Non-code or insufficient rating T&P valve
installed
T&P installed in the cold water line
T&P installed a distance from the tank, such
as in the hot outlet line
T&P has been altered or repaired
T&P valve drain line is plugged or restricted
Tips for the Temperature and Pressure
Relief drain line:
Run to a safe place of disposal (floor drain or
outside)
Drain piping should be the same size as the
valve discharge through its entire length
Pitch downward from the valve
Terminate 6 inches above the floor drain
No longer than 30 feet
Not use more than four elbows
Do not install a shut off valve in the drain line
Terminate unthreaded
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Technical Competence, Product Confidence
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Page 3
TECHNICAL SERVICE DEPARTMENT
Technical Service Bulletin
1-800-432-8373
Temperature And Pressure Relief Valves
Discharge of the T&P valve may indicate that an unsafe temperature or pressure condition exists.
Contact a licensed plumber immediately!
How to replace the Temperature and Pressure Relief Valve
CAUTION: Draining your water heater for this procedure may put you at risk of being scalded by hot water.
Please be careful when working on your water heater.
1. Turn the power OFF to the water heater at the circuit breaker
(electric heater) or main gas line (gas heater).
2. Fasten a length of garden hose to the drain valve at the
bottom of the heater. Put the other end of the garden hose in the
nearest floor drain or snake it outside the home.
3. Close the shut off valve at the cold water inlet line.
4. Open the temperature and pressure relief valve at the top of
the heater. Now open the drain valve and allow the water to
drain.
CAUTION: THE WATER WILL BE HOT...........BE SURE
NO ONE IS NEAR THE DRAIN HOSE OR THEY COULD
BE SCALDED.
5. When the water stops, close the drain valve and remove the
hose.
6. Remove the old temperature and pressure relief valve. You
will need to remove the drain tube apparatus that carries the
discharge water to the drain pan or outside your home. You may
get some additional water draining from the spud. Have some
rags handy. Replace with a new temperature and pressure relief
valve. It is a 3/4 inch National Pipe Thread (NPT) valve. You
may find one at any plumbing house or home store. Use pipe
sealer or Teflon tape to seal the threads. Make sure the new
temperature and pressure relief valve is in the OPEN position.
7. Open a hot water faucet somewhere in the home. Open the
shut off valve at the cold water inlet line. You will hear the
heater start to fill.
8. When you have a steady stream of water from the
temperature and pressure valve tube, close the valve; when you
have a steady stream of water from the hot water faucet, turn the
faucet off.
9. Turn the power ON to the water heater at the circuit breaker (electric heater) or main gas line (gas heater; relight
pilot if required). Allow the water heater to recover. Check the temperature and pressure relief valve one more time
to make sure it is tight.
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