A certified home inspector checking a basement window at a home in Greeley, Colorado.

What is a TPR Valve?

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What is a TPR Valve?
by: Joshua Luttmer

TPR valves are crucial for the safety and operation of your water heater. These safety devices can be found on water heaters and boilers in homes and businesses. TPR valves will release water if the pressure or temperature of the water tank is higher than safe levels.

Temperature sensors and safety devices, such as TPRs, can malfunction and cause water to become superheated (above the boiling point). When the tank bursts, the water will expand rapidly into steam and increase in volume up to 1600x. A heating tank can be propelled through multiple floors like a rocket, potentially causing injury to individuals and property damage.

Although water heater explosions are rare because, they do still happen.  And while the risk may seem low, it is a serious condition should it occur.  Thankfully, in order for a severe malfunction such as explosion occur, outright negligence or  obsolete and malfunctioning equipment is normally required to induce such an event.

How to test a TPR Valve

Leakage and malfunctioning TPR valves are two of the most common problems associated with water heaters. TPR valves can fail due to corrosion, debris, or freezing temperatures.

To ensure that your TPR valve is working correctly, we recommend checking it every 6 months.

  • Simply lift the TPR valve several times and it will test. The attached brass stem should be lifted and hot water should flow out of the drainpipe.
  • As the valve opens, you should hear a gurgling sound. This is the water being released into the drain tube. Contact a plumber if water is not coming out or if it's just a trickle.
  • If the water is still flowing out of the valve, you can continue raising and lowering the valve to remove any debris.
  • To avoid overheating and scalding, reduce the thermostat temperature of the water heater to 120 degrees Fahrenheit after the test. Ideal water pressure should range between 50-60 psi.
  • TPR drainpipes should be made from heat-resistant materials such as copper. Contact a professional plumber immediately if the drainpipe leaks or causes any leaks near your water heater.
  • Ideal drainpipes should be placed between 6-24 inches and 24 inches above the ground.

What are the most common TPR Valve defects?

Most defects found during a home inspection relating to the TPR Valve are due to faults with the discharge pipe. The common defects related to the TPR Valve discharge pipe include the following:

  1. no discharge pipe installed at all.
  2. too short of a discharge pipe.  It must not extend more than 6 inches (152mm) from the floor or waste receiver.
  3. use of unapproved materials like PVC.  CPVC, copper and polyethylene or galvanized steel would be approved.
  4. improper sizing of discharge pipe. It should not be less than the diameter of its outlet (usually no less than 3/4")
  5. installed in a way that cannot gravity drain.
  6. has a trap installed which can contaminate the water supply if it were to backflow.
  7. discharging in areas other than a floor drain or an indirect waste receiver, or outside.
  8. the system being connected directly to the drainage system which can contaminate the water if it were to backflow.
  9. no air gap at discharge point.

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