What maintenance does a water heater need, and how often?

Safety before any maintenance

If you smell gas near the water heater, stop. Leave on foot, avoid anything that can spark, and call the gas utility and 911 from a safe place^[9].

Maintenance on this page means owner-level tasks the makers describe in their manuals: draining and flushing, checking filters and vents, reading settings. Gas valves, gas lines, venting changes, electrical wiring and relief valve replacement are licensed work. A.O. Smith's own advice is to call a professional if you are not comfortable working around gas or electricity^[1].

The schedule at a glance

Task	Tank (gas or electric)	Tankless	Heat pump (hybrid)	Source
Flush sediment	At least once a year	n/a	At least once a year (it has a tank)	A.O. Smith[1], Rheem[2]
Descale the heat exchanger	n/a	About yearly in slightly to moderately hard water; more often in harder water	n/a	Rinnai[3]
Inspect anode rod	Yearly; replace every 3 to 4 years or when worn	n/a	Check your manual	A.O. Smith[1], Rheem[2]
Relief valve check	Yearly by the owner; a pro every 2 to 5 years	Per the manual	Yearly by the owner; a pro every 2 to 5 years	A.O. Smith[1]
Clean the water inlet filter	n/a	With each flush, or when flow drops	n/a	Rinnai[3], Rheem[5], Navien[4]
Clean the air filter	n/a	Every 3 to 4 months (Navien)	Every 6 to 12 months; 1 to 3 months in dusty homes or with pets	Navien[4], Rheem[6]
Check vent terminals and condensate line	Gas: look for damage or blockage	Each season, especially after snow	Keep the condensate drain clear	Rinnai[3]
Check house water pressure	Aim for 40 to 60 psi	Aim for 40 to 60 psi	Aim for 40 to 60 psi	Rheem[2]

Your owner's manual wins over any general schedule. If you lost it, the model number on the rating plate will find it on the maker's site.

Tank water heaters

Flush the sediment. A.O. Smith says most tank heaters need flushing at least once a year, more often in hard water^[1]. Rheem gives the same yearly interval and says removing sediment improves efficiency and extends tank life^[2]. Sediment is also what causes popping and rumbling. Step-by-step: how to flush a tank water heater.

Check the anode rod. The anode is a sacrificial rod that corrodes so the tank does not. A.O. Smith says to inspect it yearly and replace it if it is deteriorated or shows several inches of bare core wire^[1]. Rheem suggests replacement every 3 to 4 years^[2]. Softened water wears it faster. See anode rod and checking and replacing the anode rod.

Check the relief valve. The temperature and pressure relief valve is the tank's last line of defense. A.O. Smith says the owner should check it once a year and a professional should inspect it periodically: every 5 years in its manual^[1], every 2 to 4 years on the label of the valve itself. Follow the label on your valve. The water that comes out is scalding hot, so make sure the discharge pipe runs to a safe spot first. Rinnai's tankless manual takes a stricter line and says relief valve testing should only be done by a trained and qualified professional^[3]. If the valve drips afterward or will not reseat, call a plumber; never cap or plug it. See relief valve leaking or dripping.

Check the expansion tank, if you have one. Homes with a check valve, backflow preventer or pressure-reducing valve on the water line need thermal expansion control under the model code^[8]. A failed expansion tank shows up as a dripping relief valve. See expansion tank.

Tankless water heaters

Descale the heat exchanger. Scale is the top preventable tankless failure. Rinnai recommends a yearly flush for residential units in slightly to moderately hard water and treatment in harder water^[3]. The units tell you when: Rinnai shows LC or SS, Rheem shows 1L, and Navien shows E760^[3][5][4]. Rinnai states that scale damage is not covered by its warranty^[3]. Full details: how to descale a tankless water heater.

Clean the filters. Every tankless unit has a cold water inlet filter, and the makers clean it as part of the flush^[3][4][5]. Navien units also have an air intake filter that should be cleaned every 3 to 4 months; a clogged one stops the unit with code 110^[4].

Keep vents and the condensate line clear. Rinnai says to keep snow and ice away from the vent terminal and the condensate drain, and to call a qualified professional if the vent is blocked and cannot be easily cleared^[3].

Plan for freezing. Rinnai's SENSEI RX manual says the unit protects itself from freezing down to -22 F indoors and -4 F outdoors, out of the wind, only while it has power, and should be drained if power or gas is lost in a freeze^[3]. See vacation and freeze protection.

Heat pump (hybrid) water heaters

A heat pump water heater is a tank with a compressor on top, so it needs the tank tasks above plus care for the heat pump. Rheem recommends cleaning the air filter every 6 to 12 months, every 1 to 3 months in dusty homes or homes with pets, and whenever the control panel or app prompts you^[6]. A dirty filter cuts airflow, and with it efficiency. Keep the condensate drain clear, and keep the space around the unit open as the manual specifies.

Settings worth checking once a year

• Temperature. A.O. Smith recommends a setting no higher than 120 F to balance scald safety against bacteria^[1]. See best temperature setting.
• Water pressure. Rheem suggests keeping house water pressure between 40 and 60 psi^[2]. A plumber can test it with a gauge on a hose bib.
• Vacation mode. Many units have one. Use it instead of switching off gas or power for a short trip.

Hard water changes everything

Hard water speeds up sediment in tanks and scale in tankless heat exchangers. Rinnai's table recommends a softener or scale control system above 61 mg/L of hardness and requires one above 200 mg/L for its tankless units^[3]. If your area has hard water, shorten every flushing interval above and see the hard water maintenance plan.

What maintenance costs

HomeGuide's national ranges (August 2025)^[7]:

Service	Typical cost
Tank flush by a plumber	$75 to $250
Tankless flush and descale	$75 to $300
Anode rod replacement	$150 to $350
Tune-up (may include flush, filter cleaning, anode, relief valve and vent checks)	$100 to $500

Ask what a tune-up includes before you book; the scope varies.

The guides in this section

• Annual maintenance checklist: one page to print and tick off.
• How to flush a tank water heater
• How to descale a tankless water heater
• Checking and replacing the anode rod
• Best temperature setting
• Vacation and freeze protection
• Hard water maintenance plan

When to call a pro

• The relief valve drips after a test, or the anode fitting will not turn.
• A tankless scale or service code and no isolation valves on the unit.
• Any maintenance that requires opening a gas appliance's cover, or touching gas or electrical connections.
• A tank past 8 to 10 years that has never been flushed: get an opinion before disturbing it.