Effective 9 November 2026.
Water Heater Handbook gives general information only. It is not professional advice, and it is not a substitute for a licensed plumber, gas fitter or electrician who can see your heater. If you smell gas, leave the building and call 911 or your gas utility from outside.
General information only
Everything on Water Heater Handbook (waterheaterhandbook.com) is general information, published to help readers understand how home water heaters work, what their makers say about them, and what the federal rules and model codes say. It is not plumbing, gas, electrical, engineering or any other professional advice, and it does not take your heater, your piping, your venting, your wiring, your home or your local rules into account.
Not a plumber, gas fitter, electrician or maker
Water Heater Handbook is not a plumber, a gas fitter, an electrician, a heating contractor, a water heater maker, a retailer or a utility. It does not install, inspect, repair or sell water heaters or parts, and it does not refer anyone to a plumber, an installer, a retailer or a product. Makers named on our pages are named as the source of their own documents; we are not affiliated with them, and they have not reviewed our pages.
We never diagnose your heater
Nothing on this site says what is wrong with your heater, whether it is fine to keep using, whether to repair or replace it, whether a job is within your skills, or whether an installation meets your local code. A symptom page explains the causes a maker lists and the checks the maker gives owners; it cannot see your heater. Those decisions are yours, with help from someone who can look at the heater itself.
The label on your heater comes first
Water heaters differ by maker, model and year: standing pilots, piezo igniters, electronic controls, sealed combustion chambers, power venting, one or two elements, heat pump units. A step on our pages names the maker’s document it comes from, and it describes that maker’s heater. Where the lighting label, rating plate or manual on your own heater says something different from our page, follow your heater’s label and manual. Where they say to stop and call a qualified service technician, stop. Makers publish their manuals on their own websites, found by the model number on the rating plate.
Gas
Gas leaks can cause fires and explosions, and a heater that burns or vents badly can fill a home with carbon monoxide, which you can’t see or smell. If you smell gas, don’t switch anything on or off, don’t use a phone or start a car near the smell, leave, and call 911 from a neighbor’s house or another place well away (PHMSA, read 9 November 2026); the makers’ labels also say to call your gas supplier from a neighbor’s phone. If a carbon monoxide alarm sounds or anyone has symptoms such as headache, dizziness, nausea or confusion, get everyone into fresh air and call 911 (CPSC, read 9 November 2026).
Many gas repairs are reserved by the makers for a qualified service technician, and some makers tell owners not to attempt repair of the gas control, burners or gas piping at all. Where a page describes a gas repair, it says which maker’s document gives the steps, quotes that maker’s own qualified-person line, and shows where other makers say not to attempt the job. Describing a job is not a recommendation to do it. The CDC advises having a water heater and other fuel-burning appliances serviced by a qualified technician every year (CDC, read 9 November 2026).
Electricity
An electric water heater’s wiring can give a fatal shock. The makers’ manuals start every electrical step with the power off at the breaker or fuse, and A. O. Smith’s electric guide (100309797 Rev B, September 2020) adds checking that the power is off with a tester before touching anything. The makers also warn against switching the power on before the tank is full of water, because an element that heats in air burns out. Makers differ on what owners may do: one maker’s guide gives owners element and thermostat replacement, while others tell owners not to attempt repair of elements, thermostats or wiring. Our pages say whose manual each step comes from.
Scalding water
Hot water burns. The Consumer Product Safety Commission says most tap water scald injuries and deaths are among older people and children under five, urges households to lower their water heaters to 120°F, and says that water at 150°F can cause a third-degree burn in most adults in about 2 seconds, at 140°F in about 6 seconds and at 130°F in about 30 seconds (CPSC Publication 5098, read 9 November 2026). The CDC says a setting of 130°F to 140°F can kill germs such as Legionella but raises the risk of burns, and that above 120°F, thermostatic mixing valves at the tap help avoid burns (CDC, read 9 November 2026). Water from a drain valve, a relief valve or a flush hose can be scalding. Pages on temperature give both agencies’ advice; the setting is your decision.
Pressure and the relief valve
A storage water heater is a tank of hot water under pressure. Its temperature and pressure relief valve lets water out if the temperature or pressure gets too high. Never plug, cap or remove a relief valve, and never block or shorten its discharge pipe. When you test the valve as the manual describes, keep everyone away from the outlet and make sure the discharge runs where hot water can’t hurt anyone or damage anything. If the valve is discharging large amounts of very hot water, A. O. Smith’s gas guide (100263112, January 2015) says to turn the gas supply off and call a qualified person; follow your own heater’s manual.
Heaters that have been under water
A. O. Smith’s and Rheem’s manuals say a gas water heater that has been under water must be replaced; Bradford White’s says a qualified service technician must inspect it and replace any part of the control system that was under water. Never relight a heater that has been flooded. Never store gasoline, solvents or other flammable liquids near a gas water heater, as the makers warn.
Codes, permits and licensing
Building, plumbing, gas and electrical codes are adopted by states and local governments, often with their own amendments. Where our pages cite the International Residential Code, they cite it as the model code, by section and edition, not as the law where you live. Some states and cities require a permit, or a licensed plumber, gas fitter or electrician, for work on a water heater. In Massachusetts, for example, gas fitting work needs a permit, and permits are issued only to properly licensed individuals (248 CMR 3.05, read 9 November 2026). We have not read every state’s and city’s rules. Ask your local building department before you start, and never treat our pages as saying a job is allowed where you live.
Warranties
A repair, a removed part or the wrong replacement part can void a maker’s warranty. A. O. Smith and Bradford White, for example, say that removing the anode rod except to inspect or replace it voids the tank warranty, and Bradford White’s electric manual says element failure from dry firing is not covered. Read your heater’s warranty, and ask the maker before a repair if you are unsure.
Rules and figures change
Makers revise their manuals and labels. The Department of Energy’s efficiency standards change on set dates, ENERGY STAR revises its criteria, the model codes come out in new editions, tax credits and rebates start and end, and energy prices change every year. Each step and figure on this site shows its source and the day we read it, and it may have changed since. Check the current version with the original source before you rely on it.
Tools give estimates
Calculators and lookup tools do arithmetic on what you enter and show the methods, tables and assumptions they name. Their results are estimates. A sizing result shows what a method gives for the uses you entered; it doesn’t say what heater to buy or whether one will meet your needs. An energy cost result uses the prices and efficiency ratings shown, not your bills. An age lookup shows what the maker’s serial number format gives, and where a format repeats, every date it could mean; it can’t confirm when your heater was made or installed. A fit check compares your figures with the guidance it names; the maker’s installation manual for your model decides. Defaults that are our assumption are labelled, and you can change them.
Accuracy
Pages are checked against the sources they cite, but no check catches everything. Check important details with the original source before you rely on them. See also our terms of use.
How our content is made
Every page is fact-checked against its sources before it is published. Pages appear under the Water Heater Handbook name. Our editorial policy and how we check page explain the process.
Advertising and independence
Water Heater Handbook is free to read and funded by display advertising. Advertisers have no say over what we publish, and an ad on a page, including an ad for a maker, a retailer or a plumber, is not an endorsement or a referral. We use no affiliate links, accept no paid placements or maker sponsorship, sell no leads, rank no products and make no referrals to plumbers or installers. Names of makers, agencies and other organizations are used only to identify them.
External links
We link to makers’ manuals, federal rules, agencies, model codes and other websites so you can check what we say. We do not control those sites and are not responsible for their content.
Questions and corrections
If you think something is wrong, email contact@waterheaterhandbook.com with the page address and a source, and we will look at it. We can’t diagnose a reader’s heater or recommend plumbers, installers or products. See also our corrections page.