| Water Heater TPR Valve |
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If not allowed to properly discharge, this excess temperature and pressure will eventually cause the tank to
explode. One such tragedy occurred in Spencer, Oklahoma at the Starr Elementary School on January 9, 1982
where six children and a teacher were killed when the school’s water heater exploded with the force and effect
of two pounds of dynamite. This occurred due to a malfunctioning TPR valve.
Click here to see a water heater explode!
Many water systems do not have back-flow prevention, which will allow the excess pressure to feed back into
the water supply. This may keep the water heater from exploding, however boiling water or steam could be
discharged through any fixtures that might be opened while the water heater is in an over-pressure, over-
temperature failure mode.
TECHNICAL DETAILS
The discharge piping serving a TPR valve should:
FOR DIFFICULT TO DRAIN LOCATIONS
If the location of a gas fired water heater does not allow for a convenient gravity drain (e.g. in a below grade
installation, center of a building with a slab foundation) a WATTS 210 automatic gas shut-off valve can be
used to reduce the risk of damage. The Watts valve senses an over-temperature condition and turns the gas
supply to the unit off. A pressure relief valve is still required, but can be installed at a different location.
See Floodstop Products for devices that can turn off the water when a leak is detected
explode. One such tragedy occurred in Spencer, Oklahoma at the Starr Elementary School on January 9, 1982
where six children and a teacher were killed when the school’s water heater exploded with the force and effect
of two pounds of dynamite. This occurred due to a malfunctioning TPR valve.
Click here to see a water heater explode!
Many water systems do not have back-flow prevention, which will allow the excess pressure to feed back into
the water supply. This may keep the water heater from exploding, however boiling water or steam could be
discharged through any fixtures that might be opened while the water heater is in an over-pressure, over-
temperature failure mode.
TECHNICAL DETAILS
The discharge piping serving a TPR valve should:
- Be constructed of an approved material such as CPVC, copper, polyethylene, galvanized steel,
polybutylene, polypropylene, or stainless steel. - Not be reduced in size from the outlet of the valve it serves (usually no smaller than 3/4").
- Be as short and as straight as possible so as to avoid undue stress on the valve.
- Be installed so as to drain by flow of gravity.
- Not be trapped.
- Discharge to the floor, to an indirect waste receptor, or to the outdoors.
- Terminate within 6 inches (152 mm) of the floor or waste receptor.
- Not discharge in a manner that could cause scalding.
- Not discharge in a manner that could cause structural or property damage.
- Discharge to a termination point that is readily observable by occupants because discharge indicates
that something is wrong. - Be piped independent of other equipment drains, water heater pans, or relief valve discharge piping to
the point of discharge. - Not have valves anywhere.
- Not have tee fittings.
- Not have a threaded connection at the end of the pipe so as to avoid capping.
FOR DIFFICULT TO DRAIN LOCATIONS
If the location of a gas fired water heater does not allow for a convenient gravity drain (e.g. in a below grade
installation, center of a building with a slab foundation) a WATTS 210 automatic gas shut-off valve can be
used to reduce the risk of damage. The Watts valve senses an over-temperature condition and turns the gas
supply to the unit off. A pressure relief valve is still required, but can be installed at a different location.
See Floodstop Products for devices that can turn off the water when a leak is detected
| Brady Home Inspection Eureka, CA 707 444-9922 ralph@bradyinspects.com |
Water Heater Temperature/Pressure Relief (TPR) Valve
INTRODUCTION
Improperly installed TPR valves are one of the most common defects
noted on inspections.
Domestic water heaters are required to have a temperature and
pressure relief valve. This relief valve provides protection in the event
that the water heater thermostat or gas valve malfunctions, causing
excess pressure/temperature. Modern water heaters are
manufactured with a valve fitted for the specific unit. To minimize the
risk of personal injury and/or property damage, the valve drain should
be run to the building exterior. The termination point should be in an
area visible to the occupants to alert them of any problems.
INTRODUCTION
Improperly installed TPR valves are one of the most common defects
noted on inspections.
Domestic water heaters are required to have a temperature and
pressure relief valve. This relief valve provides protection in the event
that the water heater thermostat or gas valve malfunctions, causing
excess pressure/temperature. Modern water heaters are
manufactured with a valve fitted for the specific unit. To minimize the
risk of personal injury and/or property damage, the valve drain should
be run to the building exterior. The termination point should be in an
area visible to the occupants to alert them of any problems.