Keeping a tank water heater going comes down to five jobs: checking the temperature, testing the relief valve, flushing out sediment, checking the anode rod and, now and then, draining the tank. None opens the burner area or a gas fitting, but all happen next to scalding water, a pressurised tank, a gas control or 240-volt wiring, so every page here follows the maker’s own manual, stop points included. The makers’ intervals differ; we show them side by side, not averaged.
General information, not professional advice. Gas, 240-volt power, scalding water and a pressurised tank can hurt you. Follow the label and manual on your own heater; where they say to stop and call a qualified technician, stop. Codes and licensing rules are set locally.
Before any job on a gas heater: if you smell gas, don’t start. Leave, and call 911 or your gas utility from well away (PHMSA). A heater that has been under water is not a maintenance job: A. O. Smith and Rheem say replace it, and Bradford White says have a qualified service technician inspect it. What to do about a gas smell, a CO alarm or back-drafting is on gas smell or carbon monoxide near a water heater.
Start with the rating plate and the manual
The rating plate on the side of the tank gives the maker, model number and fuel; on a gas heater, the lighting label tells you how it lights. Find that model’s manual on the maker’s own website. Details differ from heater to heater: the anode can sit in its own fitting or in the hot outlet, a drain valve may open with a knob or a screwdriver, and Bradford White’s gas dials turn opposite ways on its mechanical and electronic controls. Where your label and manual differ from our pages, your heater wins.
Then find the gas control knob (or the breaker), the manual gas shut-off valve and the cold water valve before you need them.
The five jobs, in a sensible order
1. Measure the temperature
CPSC urges 120°F for every home, and its method is a candy or meat thermometer under a hot tap first thing in the morning. Its burn times explain why: most adults get third-degree burns from 150°F water in 2 seconds, 140°F in 6 seconds and 130°F in 30 seconds, and even 120°F can do it in 5 minutes (CPSC Publication 5098). A. O. Smith and CDC name reasons to go higher, each with the same condition: mixing valves at the taps. Dial marks and the gas and electric steps are in what temperature to set a water heater.
2. Test the relief valve once a year
The temperature and pressure (T&P) relief valve has a lever near the top of the tank and a pipe running down from it; it lets water out if the tank gets too hot or the pressure too high. Every maker asks for the lever to be lifted at least once a year. Check the discharge pipe first: if it is missing, capped or runs uphill, don’t test the valve. Then, with no one in front of the pipe’s end, lift the lever; hot water should flow freely and stop when you let go. What each result means is in the T&P relief valve and how to test it. Never plug or cap a dripping valve: see a relief valve that drips or leaks.
3. Flush out the sediment
Minerals in tap water settle on the tank bottom; A. O. Smith says how much depends on how hard the water is and how hot the tank is set, and that draining it extends the heater’s life. A flush is a partial or full drain through the drain valve with a garden hose, then cold water run through the open drain until no more sediment comes out. How to flush a water heater gives the gas, electric, power-vent and heat pump steps from each maker’s manual.
4. Check the anode rod
The anode is a metal rod hanging inside the tank that corrodes on purpose so the steel tank doesn’t. Rheem’s test is more than 6 inches of bare core wire showing at either end. All three makers say a tank run without an anode loses its warranty, so the rod always goes back in. The water heater anode rod shows where it sits, who should check it, and A. O. Smith’s owner steps.
5. Drain the tank completely, when you need to
A full drain isn’t routine. The manuals call for it before freezing weather with the heater off, before some repairs, when a relief valve won’t stop running, and when the old heater comes out. How to drain a water heater covers emptying it, leaving it empty for a cold season, and a drain that won’t drain.
How often: what each source says
| Source | Flush | Anode | Relief valve lever |
|---|---|---|---|
| A. O. Smith gas, electric and hybrid guides (2015 to 2024) | After the first 6 months, then at least once a year (more often with a lot of sediment or hard water) | After the first 6 months, then at least once a year | At least once a year |
| Rheem gas and electric manuals (AP23698, 2023; AP17547-1, 04/15) | A few quarts every month | Removed once a year for inspection | At least once a year |
| Bradford White gas and electric manuals (REV 08/26) | A gallon every month | Every 2 years | At least once a year |
| DOE Energy Saver (Internet Archive copy, 1 May 2026) | A quart every 3 months | Every 3 to 4 years | Every 6 months |
DOE’s figures come from the Internet Archive copy of its Energy Saver page. A. O. Smith’s first look at six months shows how much sediment your water leaves and how fast it uses up a rod. A. O. Smith also puts the anode check in the middle of its drain-and-flush routine, so the cold water goes off only once.
Rules that run through every job
- Hand only on the gas control. The lighting labels say never use tools on the knob; if it won’t turn by hand, don’t try to repair it: call a qualified service technician.
- Full tank before gas or power. A. O. Smith says run a hot tap full for at least three minutes after refilling, so the air is out. An electric element switched on in a tank that isn’t full burns out, and Bradford White and Rheem don’t cover that under warranty.
- Relight by the label on your heater. If the pilot won’t stay lit after several tries, the labels say turn the knob to OFF and call. Label by label: relighting a water heater pilot light.
- After two weeks or more unused, the makers warn that flammable hydrogen can build up: run the kitchen hot tap for several minutes before using any electrical appliance connected to the hot water, with no flame or smoking nearby.
Who each maker says should do it
A. O. Smith’s current guides print the flush and anode check as owner steps, and say to contact a qualified person if you can’t do them. Rheem puts the yearly anode removal in the user’s routine. Bradford White lists its routine maintenance as work for a qualified service technician and asks for a yearly inspection by one. The yearly relief valve lever test is the owner’s job in A. O. Smith’s, Rheem’s and the valve tag’s instructions; taking the valve out to inspect it is for a qualified person.
CDC advises having a gas water heater serviced by a qualified technician every year. Gas-side work (control, burner, gas line, vent) is a different matter, and some states and cities require a licensed gas fitter or plumber, or a permit: ask your building department.
Heat pump and tankless heaters
A heat pump (hybrid) water heater is a tank, so all five jobs apply; A. O. Smith’s hybrid guide adds cleaning the air filter and condensate pan.
A tankless heater has no tank to flush; its routine job is descaling the heat exchanger, and Rinnai’s N series manual says the heater must be inspected every year by a trained and qualified professional. See tankless water heater maintenance and descaling.
When to stop and call
- A gas smell or a CO alarm: leave and call from outside.
- The relief valve keeps running: turn off the gas or power, close the cold water valve, keep everyone away from the pipe’s end, and call a licensed plumber.
- The relief valve gives little or no water when tested, or the tank won’t drain: gas or power off, and call a qualified person.
- Water seems to come from the tank itself: see what the leak’s location tells you.
- The heater has been under water, or anything looks different from your heater’s label or manual.
Your next step
Find your model’s manual, check a hot tap with a kitchen thermometer, and look at where the relief valve’s pipe ends. Then plan the flush and anode check together, on the schedule your manual gives.
Sources checked on 9 November 2026: the maker manuals cited on each page in this section; CPSC Publication 5098; CDC; PHMSA; DOE Energy Saver (archived 1 May 2026).
