Hot Water Heater Operation and Maintenance to Improve Safety and Efficiency
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Hot Water Heater Operation and Maintenance to Improve Safety and Efficiency

replacing temperature pressure relief valves and anode rods

Hot water heaters are an indispensable appliance in the modern home, but can also cause considerable damage to the home and its occupants if it is not maintained properly. This article will go over hot water heater's major components, inspection points, and repairs.  This article is geared towards gas-fired hot water heaters as these include additional components such as baffles, vents, and burners.

Hot Water Heater Components

Cold Water Supply Valve – this item is to control flow of water to the water heater.

It should be a full bore gate valve or ball valve. Without a cold water shut-off, the water main must be used. Most areas require cold water shut off within arms length of the front of the water heater.

Temperature / Pressure Relief (TPR) Valve – Inside the TPR valve is a spring loaded disc that will open should the temperature reach 210 degrees or the pressure reach 150 lbs. TPR valves are mandatory on water heaters. The correct location for the valve is within the top six inches of the tank. Some are top mounted; others are side mounted. Gas water heaters without TPR valves have been known to go through the roof of a home. Relief valves should also have a discharge vent line terminating near the floor. Some areas, however, do require them to be piped outside. In addition the pipe must be full-sized, usually 3/4 inch, and never threaded at the outlet end nor trapped in any way. If piped to a sink or floor drain, it must have an air gap between the outlet end and the rim of the sink or drain.

Gas Line Shutoff – Should an emergency arise, the gas shut off valve can be used to shut down the water heater immediately. It can also be used to shut off the gas for servicing or repairs.

The inspector may want to barely turn the gas valves, just enough to determine they are not frozen shut, but no more.

Drain Valve – Draining a few quarts off the bottom of the tank once a year (or as often as manufacturers suggest) may prolong the life of the water heater. Over time sediment and sludge build up at the base of the tank. This sediment contributes to the deterioration of the tank and also prevents heat transfer. The drain valve is generally not located directly at the base of the tank, so some sludge will remain no matter how often it’s drained. The popping noises sometimes heard while a water heater is operating can most often be attributed to the sludge buildup. This sediment may also block the valve during testing, in which case it will need to be replaced.

Thermostat Control – The temperature of domestic hot water should not be above approximately 120° F to help prevent scalding. This corresponds to a dial setting of about halfway (needle pointing straight up.) Turning the thermostat all the way up could result in temperatures of approximately 180° F. Many newer gas controls have built-in stops to prevent thermostats from being set too high. This type of control is usually set at 140° F. Temperature settings for residential heaters should be around 130° F to kill Legionella bacteria.

Sacrificial Anode – Water will always try to corrode something. In every water heater there is an anode, usually composed of aluminum, zinc-aluminum alloy, or magnesium, which will most likely corrode before the tank begins to corrode. Once this anode is completely gone or is removed, the tank will begin to corrode. Replacement of the anode is a simple process and can greatly increase the life span of the water heater. Sometimes it has to be removed and replaced with a rod of another composition because of the adverse chemical reactions to the rod supplied.

Burner – Located at the bottom of the heater where gas, or oil, is burned to heat the water inside the tank. The burner is set under the steel tank and flue gases rise through a tube and baffle that runs through the tank.

Baffle – Inside the tank vent for the water heater is a helical shaped baffle. The purpose of the baffle is to help deflect heat to the tank and increase the efficiency of the burning process. Often when carbon monoxide is discovered at the water heater it is because this baffle has fallen down into the flames at the base of the water heater.

Vent Pipe – Galvanized metal ducting that removes combustion gases from the burner as it passes through the baffle.

The Temperature Pressure Relief (TPR) Valve

If replaced, the valve must meet the requirements of local codes, but not less than a combination temperature and pressure relief valve certified as indicated in the above paragraph. The valve must be marked with a maximum set pressure not to exceed the marked hydrostatic working pressure of the water heater (150 PSI = 1,035 kPa) and a discharge capacity not less than the water heater input rate as shown on the model rating plate. For safe operation of the water heater, the relief valve must not be removed from its designated opening nor plugged.

Replacing the TPR is relatively simple. The TPR unscrews from the tank easily especially if it's been installed with pipe-thread seal tape. What's connected to it and how it was piped can complicate matters. Code requires, at minimum, a pipe leading to within about six inches of the floor to prevent injury when testing.

As to testing the relief, you accomplish this by pulling up on the handle, holding it a few seconds and letting go. Water should flow through the line while the handle is raised and stop when you let go. If there is no water flowing, it won’t stop flowing, or won't stop dripping within a few minutes after releasing the handle, the TPR should be replaced.

If sediment coats the temperature probe on the interior it will need to be replaced. This is due to dissolved minerals in the water collecting on the probe over time. This creates a thermal insulator that will prevent the TPR from tripping at its design temperature.

Anode Rod

The sacrificial anode rod is probably the most important component of the hot water heater that is never thought about, or even seen. The warranty provided by hot water heater manufacturers is based on the expected life of the anode rod. This can vary however due to water conditions and maintenance routines. The head of the anode is a 1 – 1/16 inch hex head protruding from the top of the tank. Some manufacturers use a combination rod which is attached to nipple of the hot water outlet, you will know you have this type of anode if there is no hex head apparent at the top of the tank. Due to the properties of the metal, aluminum rods are less reactive and dissolve slower than magnesium, but offer slightly less protection. There are also health concerns with aluminum that I will not go into here. Aluminum rods are also cheaper, which is why they are commonly used for anode rods. Aluminum does have an advantage over magnesium in reducing the “rotten egg” odor that occurs. Softened water will dissolve either anode more quickly due to the salt and aluminum rods will leave behind a greater amount of sediment which will need to be flushed from the tank. Hard water will consume rods more quickly and also deposit minerals on the TPR valve as discussed earlier.

Sediment Control

The process of heating hard water will cause minerals to come out of solution and be deposited on the tank bottom. This is why manufacturers recommend flushing the tank at least annually. An increase in sediment will lower the heater’s efficiency since the sediment will insulate the water from being heated and potentially overheat the bottom of the tank. Follow the instructions in you owner’s manual for this, but basically it entails opening the drain valve at the bottom of the tank slowly. I usually hook up a garden hose to the valve and run it to my sump pump pit. You can also run it to a sink or outside, even into a 5 gallon bucket if you have no other option. Since the water is hot, wear gloves to prevent scalding, also the heat may cause the hose fitting to expand and come off, so make sure that it is on tight. Run the water until clear.

An important part of flushing the tank is the dip tube. This is a long plastic (PVC) tube on the nipple of the cold water line inside the tank that brings the cold water down to the bottom of the tank to be heated. These become brittle overtime and can fall apart. Some companies sell curved dip tubes which will create a circular water flow to help direct the sediment to the drain valve. Replacing the original drain valve with a ball valve will help flush the sediment out faster. Also, after about 10 years, the dip tube can disintegrate to the point where you may find small pieces of it in your aerators of your faucets. At this point the dip tube will need to be replaced.


Look at the tank for any signs of corrosion or blackened areas near the burner. Corrosion can be coming from a leak inside of the tank or from high moisture content in the area. Blackened areas near the burner are almost always from improper combustion or back drafting. Insulation blankets can be purchased to wrap water heaters, but when blankets are installed on gas water heaters, the fire hazard may outweigh the minor if any cost savings of the wrapping. Insulated covers on newer water heaters are worthless as far as insulation goes. More often than not they pose greater fire hazards because of the proximity to the draft diverter or the combustion chamber at the base.

 Energy Use

Here is a chart describing the energy use over the life of the hot water heater. You should choose the heater that best suits your specific needs and fuel options. If you decide to lower the water temperature, every 10 degree reduction will save about 3-5% in energy costs.

From American Council for an Energy-Efficient Economy Posted: November 26, 2007


By installing an Automatic Shutoff Valve, you can not only reduce the chance of water damage and fire in your home, but you may be able to reduce your insurance premium and increase your peace of mind.

Several manufacturers have developed devices to prevent or lessen the leaks created by a tank failure. One of these is a Water and Gas Safety (WAGS) Valve by Taco, Inc., which will shut of the water and the gas to the hot water heater when it senses a leak. The cold water lines will need to be piped to the bottom of the heater and also have a drain pan installed to hold the water. When the water reaches a height of ¾ inch, a fiber element dissolves and releases a spring loaded valve which shuts off the water. In gas-fired water heaters, this action also breaks a fuse that shuts off the gas supply to the heater. It requires no outside power source.

 WAGS Valve

Watts has developed WDS FloodSafe® Water Detector Shutoff that protects the homeowner from catastrophic damage due to the water heater leaking. The FloodSafe® will detect the presence of water on the floor beneath the water heater and will automatically shutoff the water supply and power source to the water heater. There are models for gas, electric, and oil heaters, and also has an optional battery backup unit available.

 Watts WDS FloodSafe®

Most of the work described in this article can be performed by the homeowners, but when adding components to the heater, or replacing gas or electric elements, it is best to hire a professional.

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Comments (2)
jean sublett

my basement flooded and my hot water tank went out i can,t seem to get the tank to light is there something i need to do asps thank you

If the gas control valve got wet, there may not be any current being produced by the thermocouple. When you release the button after lighting the pilot, the milliamps generated by the thermocouple keep the valve open. You can try replacing the thermocouple first and see if that works, but after that you may need a new control valve and a licensed heating contractor or plumber should perform that repair. This factoid has the steps to replace thermocouples: