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Home Inspections - Hot Water Valves

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Author, Edward Robinson is vice president of Professional Engineering Inspections, Inc. He holds a degree in mechanical engineering from the University of Houston and is a TREC licensed real estate inspector in the Houston area. You may contact Professional Engineering Inspections's at (713) 664-1264.

Failed Temperature And Pressure Relief Valve.

Temperature and pressure relief valves are included on all closed-system equipment intended to produce hot water, including water heaters. The purpose of a relief valve is to prevent excessive pressure and/or temperature into the steam range, which can cause tank explosion or scalding at fixtures in the event of a control malfunction in the operation of a water heater. Unfortunately, a majority of the valves encountered during inspections are found to be non functional or have not been properly installed and may fail under actual use, which can result in catastrophic failure of the water heater. This is mostly as a result of owner negligence in not properly testing and having the valve serviced or negligence by the installer of the valve. Worse yet is the fact that many do not understand the importance of this safety device. The importance of the proper operation of the valve is underscored by information provide by ASME that over 21,000 boiler and pressure vessel accidents occur in the United States alone. Explosion of a water heater due to excessive pressure and temperature often results in severe damage to property and can result in loss of life because of people being in the proximity of the heater when it explodes with extreme violence.

Proper Installation:

The temperature and pressure relief valves on most water heaters are installed with a temperature sensor extending into the tank, near the top of the tank, and have a drain line graded downward for its full length and extending to a visible outside location, with the end of the line pointed toward the ground and within approximately 1 foot of the ground. In most cases where the valve is installed for residential use, the valves are rated to open at a temperature of 210 F and a pressure of 150 psi; however, the ratings for pressure should be below the rated pressure for the water heater in which they are to be installed. The drain line connected to the relief valve must be the same size as the valve outlet, be as short as possible, and it must have very few turns to allow pressure buildup if the valve is activated. Additionally, care should be taken when installing the elbow at the discharge line so that an elbow is not used which could allow caps or plugs to be installed on the drain line in the future. The discharge of the valve is normally installed to vent to a safe visible location at the outside of the house for safety in the event the valve should open.

Improper installations of valves may include:

  • The improper use of an unapproved drain line material. This may result in failure of the plumbing pipe if it is not rated at the temperature and pressure of the safety valve used, allowing scalding water to be discharged into the living area. The best drain line materials are copper pipe and galvanized steel pipe.
  • The use of an undersized drain pipe, a drain pipe having too many turns, or of an excessive length. These factors can prevent the relief valve from venting sufficient water from the heater in order to prevent the water heater tank from failing. Often, threaded elbows are used at the discharge point of the drain line, which may allow a plug fitting to be installed. This is seen most often if the valve begins to leak and is plugged by a homeowner.
  • The valve may be improperly installed on a discharge or inlet line at the top of the water heater. The manufacturers of most valves require that the valve be installed directly onto the tank with a sensor probe extending into the tank.
  • Improper testing of the valve. The valve should be tested at a minimum of 1-year intervals, with more frequent testing desirable. Testing of the valve ensures that it does not become clogged with corrosion or mineral deposits. Testing also ensures that the drain line does not become clogged with debris or insects.
  • Improper routing of the drain line. The drain line should be installed with a down grade away from the water heater. If the drain line is routed up, water which may periodically seep from the valve will stand against the valve, which can result in corrosion and failure of the valve to operate. Additionally, the drain line should be protected where it passes through areas where freezing could occur to prevent seepage from freezing in the drain line and causing a clog.

It is recommended by most manufactures that temperature and pressure relief valves on water heaters be tested at intervals of at least one year, with more frequent testing being desirable. It is further recommended by many manufactures that these valves be removed and inspected by a qualified plumber at intervals of not greater than 3 years. If the valves are found to be worn or defective as the result of testing and/or inspection, they should be replaced. Signs of a worn or defective temperature and pressure relief vale include:

    • A valve which does not open when the test lever is pulled with a normal amount of force.
    • Corrosion on the stem of the valve.
    • Water leaking from the valve stem.
    • Water leaking from the drain valve.
    • A valve which does not close normally after being tested.

Owners should be on the lookout for water heaters showing signs of distress which indicate a malfunction. Indications of an overheating water heater may exhibit the following conditions:

    • A discharging safety relief valve.
    • Scorched or burning paint on the skin/casing.

The recommended safe intervention is to:

    • Remove the heat source by stopping the supply of fuel.
    • Do not try to relive the pressure.
    • Do not add cool water into the vessel.
    • Do not try to cool the vessel.
    • Let the vessel cool down naturally.
    • Get away from the vessel and call a qualified repair company.

As well as having an operational temperature and pressure relief valve, it is a good idea to have a readily accessible shutoff valve for the gas supply to a gas heater or know where the controls for an electric heater are. This will make it safe and easy to turn off the fuel supply to the water heater in the event of a malfunction. In addition to frequent testing of the temperature and pressure relief valve, it is also a good idea to have your water heater inspected on a yearly basis in order to detect any need for repair before any malfunction becomes a hazard to one’s house or health.

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