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A Boiler: The Explosive Potential of a Bomb
Acoustic Emission Examination of Metal Pressure Vessels
Anatomy of a Catastrophic Boiler Accident
Austenitic Stainless Steel
Basic Weld Inspection - Part 1
Basic Weld Inspection - Part 2
Black Liquor Recovery Boilers - An Introduction
Boiler Efficiency and Steam Quality: The Challenge of Creating Quality Steam Using Existing Boiler Efficiencies
Boiler Logs Can Reduce Accidents
Boiler/Burner Combustion Air Supply Requirements and Maintenance
Carbon Monoxide Poisoning Preventable With Complete Inspection
Combustion Air Requirements:The Forgotten Element In Boiler Rooms
Creep and Creep Failures
Description of Construction and Inspection Procedure for Steam Locomotive and Fire Tube Boilers
Ensuring Safe Operation Of Vessels With Quick-Opening Closures
Environmental Heat Exchangers
Factors Affecting Inservice Cracking of Weld Zone in Corrosive Service
Failure Avoidance in Welded Fabrication
Finite Element Analysis of Pressure Vessels
Fuel Ash Corrosion
Fuel Firing Apparatus - Natural Gas
Grain Boundaries
Heat Treatment - What Is It?
How to Destroy a Boiler -- Part 1
How to Destroy a Boiler -- Part 2
How to Destroy a Boiler -- Part 3
Identifying Pressure Vessel Nozzle Problems
Inspection, Repair, and Alteration of Yankee Dryers
Inspection, What Better Place to Begin
Laminations Led to Incident
Lay-up of Heating Boilers
Liquid Penetrant Examination
Low Voltage Short Circuiting-GMAW
Low Water Cut-Off Technology
Low-Water Cutoff: A Maintenance Must
Magnetic Particle Examination
Maintaining Proper Boiler Inspections Through Proper Relationships
Microstructural Degradation
Miracle Fluid?
Organizing A Vessel, Tank, and Piping Inspection Program
Paper Machine Failure Investigation: Inspection Requirements Should Be Changed For Dryer Can
Pipe Support Performance as It Applies to Power Plant Safety and Reliability
Polymer Use for Boilers and Pressure Vessels
Pressure Vessel Fatigue
Pressure Vessels: Analyzing Change
Preventing Corrosion Under Insulation
Preventing Steam/Condensate System Accidents
Proper Boiler Care Makes Good Business Sense:Safety Precautions for Drycleaning Businesses
Putting a Stop to Steam Kettle Failure
Quick Actuating Closures
Quick-Actuating Door Failures
Real-Time Radioscopic Examination
Recommendations For A Safe Boiler Room
Recovering Boiler Systems After A Flood
Rendering Plants Require Safety
Repair or Alteration of Pressure Vessels
Residential Water Heater Safety
School Boiler Maintenance Programs: How Safe Are The Children?
Secondary Low-Water Fuel Cutoff Probe: Is It as Safe as You Think?
Short-Term High Temperature Failures
Specification of Rupture Disk Burst Pressure
Steam Traps Affect Boiler Plant Efficiency
Steps to Safety: Guide for Restarting Boilers After Summer Lay-Up
Stress Corrosion Cracking of Steel in Liquefied Ammonia Service - A Recapitulation
Suggested Daily Boiler Log Program
Suggested Maintenance Log Program
System Design, Specifications, Operation, and Inspection of Deaerators
Tack Welding
Temperature And Pressure Relief Valves Often Overlooked
Temperature Considerations for Pressure Relief Valve Application
The Authorized Inspector's Responsibility for Dimensional Inspection
The Effects of Erosion-Corrosion on Power Plant Piping
The Forgotten Boiler That Suddenly Isn't
The Trend of Boiler/Pressure Vessel Incidents: On the Decline?
The Use of Pressure Vessels for Human Occupancy in Clinical Hyberbaric Medicine
Thermally Induced Stress Cycling (Thermal Shock) in Firetube Boilers
Top Ten Boiler and Combustion Safety Issues to Avoid
Typical Improper Repairs of Safety Valves
Wasted Superheat Converted to Hot, Sanitary Water
Water Maintenance Essential to Prevent Boiler Scaling
Water Still Flashes to Steam at 212
Welding Consideration for Pressure Relief Valves
Welding Symbols: A Useful System or Undecipherable Hieroglyphics?
What is the Best Welding Process?
What Should You Do Before Starting Boilers After Summer Lay-Up?
Why? A Question for All Inspectors

Residential Water Heater Safety

Dean Jagger
Chief Inspector, Ohio

Category : Operations

Summary: The following article is a part of the National Board Technical Series. This article was originally published in the Summer 2001 National Board BULLETIN. (2 printed pages)



Residential water heaters are not typically part of our members’ jurisdictional responsibilities. As a fired pressure vessel, however, the residential water heater represents a marriage of select components that make up both a pressure vessel and a boiler. In promoting boiler and pressure vessel safety, it makes sense to use the water heater as a familiar example. Even though residential water heaters usually do not fall under our jurisdictional regulations, National Board members continue to serve as advocates for home water heater safety. As part of this ongoing effort, we present below a list of tips to keep your home’s water heater operating efficiently and safely.

Do-It-Yourself Maintenance of Electric AND Gas-Fired Water Heaters:

  • When water is heated, calcium carbonate settles to the bottom of the tank. This sediment reduces the efficiency of your water heater, as well as its storage capacity and eventually its lifespan. To combat the effects of this natural process, drain water from your tank two to four times a year (more often if you live in a hard-water area). To do this, first turn the water heater off. Then simply attach a length of garden hose to the drain valve near the bottom of the tank and empty several gallons into a floor drain or bucket. Typically the water will look rusty or brown.

    Occasionally sediment sticks inside the valve after you drain it, preventing it from resealing tightly. Opening and closing the valve a few times will usually flush the sediment out of the valve. Finally, remember to turn the water heater back on as the last step of the process.
  • On most water heater models, there is a safety device known as the temperature-pressure relief (“T & P”) valve located near the top. If an excessively high temperature or pressure were to build up in your water heater, this T & P valve is designed to open, relieving the effects of the high temperature and/or pressure and so preventing an explosion. Once a year, test it – first, make sure there is a pipe attached to the valve outlet; if not, you or your plumber can add one. Then, pull up on the handle. If water flows out of the pipe then the T & P valve is free to open.

    As with the drain valve, sediment may lodge under the valve seat after you test it, preventing it from re-sealing. If this happens, pull on the T & P handle a few times to flush the sediment away. If it still does not seal, call a qualified plumber immediately to have the T & P valve replaced. NEVER cap the discharge pipe of the T & P valve to prevent leakage.
  • For energy savings and homes with small children, many consumer safety organizations recommend setting your water heater thermostat to 120 degrees. A special word of caution, however: water temperatures below 120°F can enable unhealthy bacteria to grow inside your water heater.
  • Many homeowners insulate their water heaters, especially if located in the garage. Insulation kits designed specifically for this purpose are available. Be careful not to cover up the T & P valve, control panel, or drain. Do not cover the top of a gas-fired unit at all; also keep the pilot light access, air intake, and draft diverter free and clear.
  • A normal 50-gallon capacity water heater can hold approximately 400 pounds of water. If you live in an earthquake zone, water heater strap kits are available and in some areas even required, to help stabilize the unit and prevent it from tipping over in the event of a tremor.


Specific to Gas-Fired Water Heaters:

  • Keep the area around your hot-water tank clean and clear of combustibles. This includes accumulations of dust and dirt, paper of any type, and especially any flammable liquids. Paint thinner, cleaning agents, and gasoline are all examples of dangerous liquids that should be stored well away from the water heater. Never set off aerosol bug bombs nearby without first properly shutting off the gas supply and extinguishing the pilot light.
  • If the water heater is located in the garage, raise it so that the pilot light is 18 inches above the floor. This increased height will help prevent the ignition of any gasoline fumes which accumulate near the floor.
  • If you have any gas-fueled appliances (water heater, furnace, oven, clothes dryer, etc.) in your home, a carbon monoxide detector is imperative. The Consumer Product Safety Commission warns carbon monoxide poisoning kills 200 people each year and causes another 10,000 to need hospital treatment. This odorless, colorless gas is a potential danger with all combustion appliances.

    And if you smell gas, get out of the house immediately. Use a neighbor’s telephone to call the fire department and the gas company. The slightest spark could cause an explosion. Natural gas is lighter than air and will usually diffuse. Propane is heavier than air and will collect in low areas, such as basements.


Professional Maintenance:
Some important tasks require the expertise of a service professional (a qualified plumber, heating contractor, or gas company technician).

  • For gas- and oil-fired water heaters, burners should be cleaned once a year. Have the service professional also inspect flues and vents for cracks or loose connections which could leak deadly exhaust gases.
  • Perhaps the single most neglected component of your home’s water heater is its sacrificial anode. The anode is a magnesium or aluminum rod which is suspended inside your steel storage tank. Over time, an electrochemical reaction causes the anode rod to corrode while the steel tank remains intact. If the anode has sacrificed itself completely and there is no metal left, the electrochemical process attacks the water heater tank itself – it corrodes, and you find yourself in the market for a new water heater!

    Instead, have a qualified plumber (some localities will require plumbers to be licensed) replace your anode rod once every two to five years.
  • The service life of a T & P valve is usually three years. Even if a T & P valve looks fine from the outside, manufacturers recommend they be removed and visually inspected for accumulations of corrosion deposits. Again, the T & P valve should be replaced only by a qualified plumber. [Editor’s note: The Summer 1993 BULLETIN article, Temperature and Pressure Relief Valves Often Overlooked by Lee Doran, addresses this issue and is available by clicking on Technical Articles on the National Board homepage.]

Finally, a qualified plumber is recommended if your water heater tank is leaking. The average lifespan of both electric and gas water heaters is eight to thirteen years.

In closing, if your water heater does overheat and your T & P valve is discharging water or steam, the ONLY safe intervention is to remove the heat source by cutting off its fuel, if you can. For an electric heater, trip the circuit breaker; for a gas heater, shut off the gas. NEVER go near the water heater to try to relieve the pressure yourself. NEVER add cool water to the tank. And NEVER try to cool it by spraying it with a hose. Call a qualified plumber and allow the water and water heater to cool naturally.




Editor's note: Some ASME Boiler and Pressure Vessel Code requirements may have changed because of advances in material technology and/or actual experience. The reader is cautioned to refer to the latest edition of the ASME Boiler and Pressure Vessel Code for current requirements.


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