How to inspect and replace heat traps and temperature pressure relief valves on your hot water heater.
There are few components on a hot water heater that require periodic testing or replacement. Temperature Pressure Relief (TPR) Valves are important safety devices that should be tested annually. Heat traps are energy saving devices that prevent hot water from flowing out of the hot water heater tank when the water is not running. This article will tell you how to replace each component in the event either one fails.
Temperature Pressure Relief Valves
To test the TPR valve, lift the lever on the relief valve and carefully lower it back to its closed position. Many manufacturers state that rough handling of the relief valve test lever, such as allowing it to "snap" closed, can damage the temperature and pressure relief valve. This can create a dangerous condition that could lead to a water heater explosion.
If water does not flow freely when the TPR valve is opened, the valve should be replaced with a properly rated TPR valve. Look for the pressure, size, and extension size on the metal tag. The extension (EXT) is the length of the sensor which goes into the tank. Most are 6 inches, but can be 8 inches or more and may need to be ordered.
Temperature Pressure Relief Valve
If your TPR valve has not been tested or replaced sooner than five years, the valve should be replaced. More frequent replacement of the safety valve may be needed in areas where hard water is found or the valve is noticeably leaking.
The outlet of the TPR valve has a pipe attached to it called a discharge tube; the size must be the same as the threaded connection which is screwed into the tank, typically ¾ inch. No valve can be installed after the relief valve.
Replacing a TPR valve
1. Shut off the hot and cold water valves at the top of the water heater.
2. Drain about 5 to 10 gallons of water out of the tank to a level below the TPR valve insertion point.
3. Remove the discharge tube and unscrew the TPR from the tank.
4. Inspect the extension probe to see if there is scale build up. If there is, the probe may not function properly and you may need to have your water tested.
5. Carefully apply thread tape or pipe dope onto the threads of the TPR.
6. Screw the valve into the tank so that it is secure AND the outlet points down to the floor.
7. Install the discharge tube if required.
8. Open a few hot water faucets and then open the hot water valve. Slowly open the cold water supply to the heater to fill the tank and force the air out of the lines.
9. Turn off the faucets when no more air comes out.
10. Check for leaks.
Heat traps come in a few design configurations; the two most common designs have either a rubber flap or a metal ball. Both designs act like a check valve and prevent cold water, which is heavier than hot water, from falling out of the inlet and outlet pipes into the tank.
Heat traps valves allow water to flow into the water heater tank but prevent unwanted hot water flow out of the tank. The valves which have balls inside either float or sink into a seat, which stops convection and come in pairs. Heat Trap Valves are designed differently for use in either the hot or cold water line. Heat trap valves can reduce convective heat loss by as much as 60% and some research has shown that properly functioning heat traps can save up to 10 percent on your hot water heating costs over a year.
Heat traps are usually color coded or marked with the flow direction since the hot and cold valves are designed differently.
Flap-style heat traps (Source: Bradford White)
Ball-style Heat Traps (Source: Rheem)
Heat Trap Installation - Inserts
1. Shut off water and disconnect water connections to expose original equipment nipple combination. Drain a gallon of water out of tank.
2. Insert hot water color-coded heat trap insert into the outlet nipple of the water heater until it is fully seated in position.
3. Insert the cold water color-coded heat trap insert into the inlet nipple of the water heater until it is fully seated in position.
4. Re-connect water connections.
Heat Trap Installation – Threaded
1. Shut off water and drain a gallon of water from tank.
2. Disconnect water connections.
3. Apply thread tape to both ends of the heat trap valves and thread the hot water heat trap valve into the outlet of the water heater until tight. Follow the same process for the inlet (cold) side.
4. Connect water supply and check for leaks.
As an alternative to purchasing heat trap valves, flexible supply lines can be formed into a P or S-trap to prevent the hot water from flowing out of the tank. The hot water cannot flow back down the lower side of the trap and the cold water cannot flow up the high side of the trap.
Occasionally the ball in the ball-style heat traps can become stuck. Some heat traps can be taken apart be removing the plastic insert on one end to free the ball. It may need to be cleaned, or the seat may have a scale build up. You will know when it is stuck if you have no hot water flow.
Sometimes the ball can chatter inside the valve. If this is annoying, you may want to switch to a flap-style heat trap or other silent designs.
U.S. Department of Energy