Water Heater Maintenance: DIY Guide
Flushing sediment from your water heater tank annually is a simple DIY task that extends the unit's life significantly.
DIY-Friendly
Flushing sediment and testing the pressure relief valve are simple, no-tool-beyond-a-hose tasks anyone can do. Replacing the anode rod is a small step up but still manageable. The caveat is the fuel: on a gas unit the procedure starts by shutting the gas off and ends by relighting the appliance from the label on the tank.
Skill Level
Beginner
Time Required
30–60 minutes
Physical Demands
Low
What this costs
| Hiring it out | $100–$500 per year |
| DIY materials | $20–$60 |
| Your time | 30–60 minutes |
What moves the number
- Water hardness — Hardness sets the flush interval and the anode's life. Softened water is worse for the tank, not better — A. O. Smith calls it exceedingly corrosive and asks for annual anode inspection.
- Whether the tank still drains — A tank that flushes clear costs a hose and an hour. Consolidated sediment needs a qualified person and a de-liming agent — a service call rather than a Saturday.
- Anode access — The rod is full tank height and factory-torqued. Adequate headroom makes it a twenty-minute job; a tank in a low closet can make it impractical without moving the heater.
Run your own numbers with the cost calculator — figures last verified July 2026.
- U.S. Department of Energy — Water Heater Maintenance — retrieved 2026-07-13
Before you start
Sediment is the reason this job exists. Tap water carries dissolved minerals, a tank heats them out of solution, and the scale settles over the burner of a gas tank or crusts onto the elements of an electric one. On a gas heater the layer insulates the flame from the water, which is why an overdue tank rumbles or percolates — that is water flashing to steam under the sediment bed. A. O. Smith notes that in hard-water areas it is usually easier and cheaper to replace lime-encrusted elements than to clean them.
The interval is genuinely contested, and the answer is to follow the manual for your own heater. A. O. Smith's residential gas manual recommends the tank be drained and flushed every 6 months. Its residential electric manual takes a different line: drain and flush after the first six months of operation to see how much sediment you actually make, then, depending on the hardness of your water, repeat at least annually or more frequently. Same manufacturer, different appliance. If you have no idea what your water is like, flush at six months and let the colour of the discharge set your schedule.
Two other tasks belong on the same visit. The temperature-pressure relief valve is what stops a water heater becoming a pressure vessel, and A. O. Smith says it must be manually operated at least once a year. The anode rod is a sacrificial metal rod that corrodes so the tank does not — once it is gone the tank starts to, and that failure is a leak you cannot repair. Understand the fuel side too: on a gas heater the sequence begins by turning the gas control to OFF and closing the manual gas shutoff valve, and ends by relighting from the label on the tank. On an electric heater it begins at the breaker, and the most expensive mistake available is restoring power before the tank has refilled — A. O. Smith states that a dry-fired upper heating element is an installation error and is not covered under warranty.
Code and permits
Flushing a water heater is maintenance, not permitted work — the model administrative provisions treat repairs and part replacements that do not rearrange pipes or fixtures as exempt. But three pieces of hardware you will touch or inspect are specified by code, and they are worth checking while the tank is accessible: the drain valve, the relief-valve discharge pipe, and the gas appliance shutoff.
Model plumbing code — 504.6, Requirements for Discharge Piping § 504.6 — The relief-valve discharge pipe must not connect directly to the drainage system; must discharge through an air gap in the same room as the heater; must be no smaller than the valve outlet; must serve a single relief device; must not be trapped; must flow by gravity; must terminate not more than 6 inches above the floor or the flood level rim of the receptor; and must have no threaded end, no valves and no tee fittings.
International Plumbing Code 501.3, as reproduced at P2801.2 § 501.3 / P2801.2 — A drain valve for emptying must be installed at the bottom of each tank-type water heater, with an inlet not less than 3/4-inch nominal iron pipe size and an outlet provided with a male hose thread.
Which editions of the plumbing and fuel gas codes apply is set by your state or municipality, and many jurisdictions amend the text. Manufacturer instructions govern their own appliance and are frequently stricter than the code — where the two differ, follow the manual attached to your tank.
Stop and call a pro if…
These are hard stops, not cautions. If you hit one, the job is finished for you until a licensed trade or your building department signs off on it.
A gas heater will not relight after the service
It has an ignition, thermopile, gas supply or venting problem, and repeated attempts accumulate unburnt gas in the combustion chamber.
Who to call
A qualified service technician or your gas supplier. Leave the gas control knob OFF until they arrive.
A. O. Smith, Residential Gas Water Heaters Manual (326940-001) — Lighting Instructions § Lighting Instructions — If the appliance fails to light after three lighting attempts, turn the gas control/temperature knob to the OFF position and call a qualified service technician or your gas supplier.
You smell gas, or you cannot find or operate the manual gas shutoff valve
You cannot safely isolate the appliance, and this procedure begins by isolating it. A gas odour is an evacuate-and-call situation.
Who to call
Leave the building without operating any switch or valve, then call your gas supplier from another location. For a missing or seized shutoff, call a licensed plumber or gas fitter.
International Fuel Gas Code 409.5, as reproduced at G2420.5 § 409.5 / G2420.5.1 — Each appliance must be provided with a shutoff valve located in the same room as the appliance, within 6 feet (1829 mm) of it, upstream of the union or connector it serves, and provided with access.
The T&P valve will not reseat, or it discharges on its own
A valve that keeps releasing water has failed; one that opens by itself is reporting excessive temperature or pressure in the tank.
Who to call
A licensed plumber. Close the cold water inlet first, and do not cap, plug or valve the discharge line.
A. O. Smith, Residential Gas Water Heaters Manual (326940-001) — Temperature-Pressure Relief Valve § Temperature-Pressure Relief Valve — If after manual operation the valve fails to completely reset and continues to release water, immediately close the cold water inlet, drain the heater and replace the T&P valve with a properly rated one certified to ANSI Z21.22-CSA 4.4 and the ASME code. No valve or obstruction may be placed between the T&P valve and the tank.
The tank will not drain, or water leaks from the tank body itself
Consolidated sediment blocks the drain port, and forcing the valve on a full tank risks breaking it. A leak through the shell is different again — the glass lining has failed and the steel is corroding through, which has no repair.
Who to call
A qualified service person for a blocked tank; a licensed plumber for replacement if the shell is leaking. Shut the cold inlet and the fuel supply in the meantime.
A. O. Smith, Residential Electric Water Heater Guide (100264218) — Draining and Flushing § Maintenance — Draining and Flushing — Sediment may form large masses that can prevent the tank from draining. Have a qualified person use a de-liming agent suitable for potable water to remove the sediment buildup.
Safety Warnings
- • Water in the tank can be very hot — run a hot tap until the water is cool before draining, and keep clear of the hose discharge
- • On an electric heater, open the breaker or pull the fuses and confirm with a non-contact tester before servicing anything electrical
- • Never plug, cap, valve off or reduce the T&P valve's discharge line — it is the only overpressure protection the appliance has
- • Do not restore power or gas until the tank is completely full and hot water has run full stream for three minutes
- • If you smell gas, do not operate any switch or valve — leave the building and call your gas supplier from another location
Choosing your materials
| Option | Best for | Trade-off |
|---|---|---|
| Drain-and-flush only | A heater under five years old in soft or moderate water — a hose and thirty minutes. | It does nothing for the anode or the T&P valve, which determine how long the tank lasts and how safely it fails. This is the version most people do, and the reason tanks still fail on schedule. |
| Flush plus T&P test | The realistic annual service — ten extra minutes covering the only safety device on the appliance. | Testing a valve never operated can leave it weeping. That is a finding, not a failure: A. O. Smith's instruction is to close the cold inlet, drain the heater and fit a properly rated replacement. |
| Flush, T&P test and anode inspection | Any heater past its third year, and every heater on softened water. This is the version that extends tank life. | The rod is torqued in at the factory and often needs a breaker bar; on electric models A. O. Smith specifies an 11/16-inch socket with an extension after removing the cover and the foam over the rod head. Low headroom can make it a two-person job. |
Tools & Materials
Tools
- Garden hoseYou likely own
- BucketYou likely own
Materials
- Replacement anode rod (inspect per your manual's interval; replace when depleted)
- PTFE tape or pipe joint compound for the anode threads
- Replacement T&P relief valve (only if the existing one fails to reseat)
Step-by-Step
- 1
Shut down the fuel and let the water cool
10 minutes
Electric: switch off the breaker. Gas: turn the control to 'pilot' or off, then close the manual gas shutoff valve.
A. O. Smith's gas drain sequence starts with two actions: turn the gas control/temperature knob to OFF, then turn OFF the gas supply at the manual gas shut-off valve. Code requires that valve to be in the same room, within 6 feet of the appliance, upstream of the connector, and accessible — so if you cannot find it, look along the gas line within six feet before concluding it is missing. On an electric heater, open the breaker or pull the fuses and confirm with a non-contact circuit tester before working near any electrical parts.
Then let the water cool. The electric manual asks you to open a hot water faucet and run it until the water is cool before draining, specifically to reduce the risk of scalding. A tank drained straight after a heating cycle delivers water hot enough to burn in seconds.
Check your workThe burner is off or the breaker is open and verified dead, and hot water at a nearby tap is running cool.
⚠ If you smell gas at any point, do not operate any switch or valve — leave the building and call your gas supplier from elsewhere.
- 2
Connect a hose to the drain valve
10 minutes · Garden hose, Bucket
Run the hose to a floor drain or outside.
The valve is designed for this: code requires a drain valve at the bottom of every tank-type water heater with an inlet not less than 3/4-inch nominal iron pipe size and an outlet provided with a male hose thread. Route the hose somewhere that can take a full tank of very hot water, and secure it — A. O. Smith stresses that the hose must be secured before and during the entire flushing procedure, because flushing is performed with system water pressure applied to the tank.
Check your workThe hose is threaded fully onto the valve, unkinked, secured at the discharge end, and running downhill.
⚠ Old plastic drain valves crack when forced. If the handle will not turn by hand, stop — a broken drain valve on a full tank is an emergency.
- 3
Flush the tank under pressure until it runs clear
20–40 minutes · Garden hose
Leave the cold supply on so system pressure keeps water moving through the tank while the drain valve is open.
There are two different procedures in the manual and they are worth separating. To drain, A. O. Smith closes the cold water inlet and opens a hot tap to let air in, then opens the drain valve until the tank is empty. To flush, it does the opposite: leave the cold inlet open so system pressure keeps pushing water through, open the drain valve, and let the water run until it runs clean. The flush is the one that moves sediment, because the incoming cold water stirs the bottom of the tank.
Watch what comes out and let it set your schedule. If the water never clears, or the flow slows to a trickle while the tank is obviously still full, you have hit a sediment mass rather than a stuck valve — A. O. Smith's instruction there is to have a qualified person use a de-liming agent suitable for potable water.
Check your workWater leaving the hose runs clear rather than gritty, and the flow rate has not dropped over the course of the flush.
⚠ The water will be hot even after you have run a tap. Keep the discharge end away from feet, pets and plants.
- 4
Test the T&P valve and inspect the anode rod
30 minutes · Bucket
Lift the valve's test lever briefly to confirm it releases freely, then check the sacrificial rod on your manual's schedule.
The T&P valve is certified to ANSI Z21.22-CSA 4.4 and the ASME code, and A. O. Smith says it must be manually operated at least once a year. Make sure nobody is in front of the discharge outlet and that discharged water will not cause damage, then lift the lever several times; the valve should seat properly and operate freely. If it fails to completely reset and continues to release water, close the cold water inlet, drain the tank and fit a replacement marked for the heater's 150 psi working pressure with a discharge capacity not less than the input rate on the rating plate.
For the anode, the two manuals differ again: the gas manual asks for inspection after a maximum of three years and annually thereafter, the electric manual after six months and then annually, with annual inspection on softened water because the softening process substitutes sodium for magnesium and calcium and is exceedingly corrosive. Two published signs mean replace it — most of the rod's diameter under 3/8 inch, or roughly a third or more of its length showing exposed support wire.
- Clear the T&P discharge outlet, then lift the test lever several times and confirm it reseats.
- Shut the cold inlet, open a hot tap to depressurise, and drain about five gallons before touching the anode.
- Expose the rod head, break it loose, and inspect the diameter and support wire.
- Refit or replace with thread sealant and check for leaks before restoring power or gas.
Check your workThe relief valve reseats completely with no drip, and the rod is over 3/8 inch across along most of its length — or you have fitted a new one.
⚠ If the valve doesn't reseat properly after testing, replace it — don't ignore a leaking relief valve, and never cap or valve off the discharge line.
- 5
Refill completely, then restore power or gas — in that order
20–30 minutes
Close the drain valve, refill the tank fully before restoring power to an electric unit (running an empty electric element burns it out).
Close the drain valve, remove the hose, open a nearby hot water faucet to let air escape, then open the cold water inlet. A. O. Smith's refill instruction is to keep that faucet open for 3 minutes after a constant flow of water is obtained. On the electric side the wording is stronger: do not connect electrical power before the tank is completely full, because a dry-fired upper element is an installation error and is not covered under warranty. The gas equivalent is just as blunt — do not turn on the gas unless the tank is full.
Then relight or re-energise, following the lighting instructions on the label attached to the tank rather than any generic sequence, and check every joint you touched while it heats. Finally check the temperature: CPSC urges users to lower water heaters to 120°F, and A. O. Smith notes the dial is approximate, so verify with a thermometer at a tap.
Check your workHot water runs full and uninterrupted with no spitting, the heater has completed a cycle, nothing you disturbed is weeping, and measured tap temperature matches your intended setting.
⚠ If a gas heater fails to light after three attempts, turn the gas control knob to OFF and call a qualified service technician or your gas supplier.
Common mistakes
Restoring power before the tank is completely full
Why it happens
The drain valve is closed, water is going in, and the breaker is right there — a minute early feels like it cannot matter.
The fix
Open a hot tap and wait until water runs full stream for a full three minutes before touching the breaker. A dry-fired upper element is an installation error and is not covered by warranty.
Never testing the T&P valve because it might start dripping
Why it happens
Testing an old valve genuinely can leave it weeping, so leaving it alone feels like the low-risk choice.
The fix
It is the opposite. A. O. Smith requires manual operation at least once a year, and a valve that will not reseat had already failed — the test found it. Close the cold inlet, drain, and fit a replacement marked for the heater's 150 psi working pressure with a discharge capacity not less than the input rate.
After the job: care and maintenance
At least annually — every 6 months on some gas models
Flush until the discharge runs clear. A. O. Smith's gas manual recommends every 6 months; its electric manual asks for the first flush at six months and then at least annually depending on hardness.
Annually
Manually operate the T&P valve and confirm it reseats completely, with nobody near the discharge outlet.
After three years, then annually — or after six months on an electric tank
Inspect the anode and replace it when most of its diameter is under 3/8 inch or roughly a third of the support wire is exposed. Inspect annually if you have a water softener.
FAQ
How often should I flush my water heater?
Follow your own manual, because manufacturers differ even within one brand. A. O. Smith's residential gas manual recommends draining and flushing every 6 months. Its residential electric manual asks for the first flush after six months of operation to gauge how much sediment you produce, then, depending on hardness, at least annually or more frequently. If you do not know your water, flush at six months and let the discharge set the schedule.
Do I really need to test the T&P valve?
Yes — A. O. Smith says the valve must be manually operated at least once a year. It is the only protection against excessive temperature and pressure and is certified to ANSI Z21.22-CSA 4.4 and the ASME code. If it will not reseat afterwards, close the cold water inlet, drain the heater and fit a replacement rated for the heater's marked working pressure with a discharge capacity not less than the input rate on the rating plate.
When does the anode rod need replacing?
Two published signs: most of the rod's diameter under 3/8 inch, or roughly a third or more of its length showing exposed support wire. A. O. Smith's gas manual asks for inspection after a maximum of three years and annually thereafter; the electric manual after six months, then annually. Softened water depletes the rod faster. Never leave it out — the manual states the warranty is void without it.
What temperature should my water heater be set to?
CPSC urges users to lower water heaters to 120°F, both to prevent scalds and to save energy, noting that most adults suffer third-degree burns from 150°F water in two seconds, 140°F in six seconds and 130°F in thirty seconds — and that even 120°F water can cause third-degree burns over a five-minute exposure. Verify with a thermometer at a tap rather than trusting the dial, which the manufacturer describes as approximate.
Is this a gas-appliance job I should not be doing?
Flushing is maintenance, and the manufacturer publishes the procedure for homeowners. But on a gas unit the sequence begins by turning the gas control to OFF and closing the manual gas shutoff valve, and ends by relighting from the label on the tank. Two things move it out of DIY scope: a gas odour at any point, and a heater that will not relight — A. O. Smith's limit is three attempts, after which you turn the control OFF and call a qualified service technician or your gas supplier.
Sources
Every figure, clearance and code section on this page traces to one of these. Manufacturer instructions govern their own product and override anything general said here.
- A. O. Smith. Residential Gas Water Heaters — Installation and Operating Manual (326940-001) — accessed September 3, 2026.The 6-month flush recommendation, the drain and flush procedures, T&P certification and testing, and anode inspection intervals.
- A. O. Smith. Residential Electric Water Heater — Installation Instructions and Use & Care Guide (100264218) — accessed September 3, 2026.The electric interval and dry-fire warning, the breaker and tester check, the three-minute fill, and sediment masses needing a de-liming agent.
- U.S. Consumer Product Safety Commission. Publication 5098, Avoiding Tap Water Scalds — accessed September 3, 2026.The 120°F recommendation and the burn exposure times at 150°F, 140°F, 130°F and 120°F.
- UpCodes. 504.6 Requirements for Discharge Piping — model plumbing code, Chapter 5 Water Heaters — accessed September 3, 2026.Code text on relief-valve discharge piping: air gap, sizing, no traps, no valves, no threaded end, 6-inch termination.
- UpCodes. P2801.2 Drain Valves [IPC 501.3] — residential plumbing provisions — accessed September 3, 2026.A drain valve at the bottom of each tank-type heater, 3/4-inch nominal inlet, male hose thread outlet.
- UpCodes. G2420.5 Appliance Shutoff Valve [IFGC 409.5] — residential fuel gas provisions — accessed September 3, 2026.A shutoff valve in the same room as the appliance, within 6 feet, upstream of the connector, with access.
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