How to Replace an Improper TPRV Discharge Pipe

The TPRV is a safety device the prevents your water heater from turning into a rocket, and propelling through your roof. Given its importance, we are surprised at the number of discharge pipes that are installed improperly.

There are a litany of things that can be wrong with the discharge pipe. You can find the general rules for a discharge pipe at the end of this post. If you are confident with your repair skills, its an easy task replace it yourself.


8ft of CPVC pipe, CPVC primer and cement(comes in a pack of a purple can and an orange can), a CPVC to 3/4″ copper male union, Thread Seal Plumbing Tape.

(Total cost about $20)


Adjustable wrench, plastic pipe cutter, measuring tape, possibly a saw to cut the pipe first

(Total cost about $30)


1. First, make sure you turn off the power supply, whether its a breaker, a gas valve, or an oil valve.

2. Next, turn off the water at the main water shut off valve.

3. Now would be a good time to Flush Your Water Heater.

4. Remove the improper discharge pipe.

This one had to be cut before it could be removed.

This one had to be cut before it could be removed.

5. Measure from the bottom of the TPR valve to the ground and subtract 4″. The pipe can not be more than 6″ off the ground.

6. Cut your pipe to the appropriate size.

7. Follow the instructions on the CPVC cement cans and connect the union to pipe you just cut.

Richmond Home InspectorRichmond Home Inspector

8. Apply the thread seal to the union.

Midlothian home inspector

9. Install the assembly into the TPR valve.

Much Better

Much Better

10. Some TPR valves are the top of the tank. In this case, you will simply need to make one extra measurement, one extra cut, and a 90 degree angle to the pipe assembly. Do not glue the vertical pipe into the horizontal pipe until after you install the horizontal pipe into the valve!

11. Turn on the main water shut off valve and turn the breaker back on.

Here are the requirements for discharge pipes

  1. be constructed of an approved material, such as CPVC, copper, polyethylene, galvanized steel, polypropylene, or stainless steel. PVC and other non-approved plastics should not be used since they can easily melt.
  2. not be smaller than the diameter of the outlet of the valve it serves (usually no smaller than 3/4″).
  3. not reduce in size from the valve to the air gap (point of discharge).
  4. be as short and as straight as possible so as to avoid undue stress on the valve.
  5. be installed so as to drain by flow of gravity.
  6. not be trapped, since standing water may become contaminated and backflow into the potable water.
  7. discharge to a floor drain, to an indirect waste receptor, or to the outdoors.
  8. not be directly connected to the drainage system to prevent backflow of potentially contaminating the potable water.
  9. discharge through a visible air gap in the same room as the water-heating appliance.
  10. be first piped to an indirect waste receptor such as a bucket through an air gap located in a heated area when discharging to the outdoors in areas subject to freezing, since freezing water could block the pipe.
  11. not terminate more than 6 inches (152 mm) above the floor or waste receptor.
  12. discharge in a manner that could not cause scalding.
  13. discharge in a manner that could not cause structural or property damage.
  14. discharge to a termination point that is readily observable by occupants, because discharge indicates that something is wrong, and to prevent unobserved termination capping.
  15. be piped independently of other equipment drains, water heater pans, or relief valve discharge piping to the point of discharge.
  16. not have valves anywhere.
  17. not have tee fittings.
  18. not have a threaded connection at the end of the pipe so as to avoid capping.

Good job!

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