Water Heater & Tankless Maintenance Guide

Water heaters fail in one of two ways: quietly, over a decade of neglect, or all at once, on a Sunday, into a finished basement. The average tank holds 40–50 gallons and it all ends up on the floor. Draining a few gallons of sediment once a year and descaling a tankless unit every 12–18 months is maybe two hours of work annually — and it's the difference between a unit that lasts its full life and one that quits at year eight. Here's the maintenance schedule for both tank and tankless, what a pro should actually do, and the warning signs that mean replace, not repair.

First: know what you have

Write these down before you do anything else — they're what a plumber asks for on the phone, and what a warranty claim requires:

• Type: tank (gas or electric) or tankless (gas or electric).
• Capacity: gallons for a tank, gallons-per-minute for tankless.
• Brand, model, and serial number from the data plate.
• Install date. If nobody knows, the serial number usually encodes the manufacture date — most brands publish a decoder.
• Warranty length — typically 6–12 years on a tank, up to 15 on tankless heat exchangers.
• Anode rod type (tank only) and the last time it was checked.

Tank water heater maintenance schedule

Every month (two minutes)

• Look at the floor around and under the unit. Any dampness, rust staining, or mineral crust means a leak that's already started.
• Check that nothing flammable or stored has crept into the clearance around a gas unit.

Every 6 months

• Test the T&P (temperature & pressure relief) valve. Put a bucket under the discharge pipe, lift the lever, let it snap back. Water should rush out and stop cleanly. If it dribbles afterward or nothing comes out at all, the valve needs replacement — this is the single safety device standing between a water heater and a genuine explosion hazard.
• Confirm the thermostat is at 120°F. Higher accelerates scale and scalds; lower risks bacteria growth.

Every year

• Flush the sediment. Hard water drops minerals to the bottom of the tank, where they insulate the burner from the water and force it to run longer and hotter. That's the popping and rumbling sound. Sediment is the leading cause of premature tank failure.
• Inspect visible connections, the drain valve, and the flue on gas units for rust or gaps.
• Test the CO detector nearest a gas or propane unit.

Every 3 years

• Inspect the anode rod. It's a sacrificial metal rod that corrodes so the steel tank doesn't. When it's gone, the tank starts rusting from the inside and the clock runs out fast. Replacing a $25 rod on schedule is the cheapest way to add years to a tank. On very hard or softened water, check every 2 years.

How to flush a tank water heater

1. Kill the power. Gas: set the valve to "pilot." Electric: switch off the breaker — an element energized in an empty tank burns out in seconds.
2. Shut the cold water supply valve at the top of the tank.
3. Attach a garden hose to the drain valve at the bottom and run it to a floor drain or outside. Expect hot water.
4. Open a hot tap somewhere in the house to break the vacuum.
5. Open the drain valve and let it run until the water is clear — usually 5–20 minutes.
6. With the drain still open, briefly open the cold supply to stir up and blast out the remaining sediment. Repeat until the runoff is clean.
7. Close the drain, reopen the cold supply, and let the tank fill completely. Air will sputter out of the open hot tap; wait until it runs steady.
8. Only then restore power or gas. Never energize a partially filled tank.

If the drain valve won't open, or opens and won't close again, stop and call a plumber. Plastic drain valves on older units are notorious for this, and it's a good time to have a brass one installed.

Tankless water heater maintenance

Tankless units skip the standby losses and the flood risk, but they trade that for sensitivity to scale. Water passes through a narrow heat exchanger at very high temperature, which is the ideal condition for mineral buildup. A neglected tankless unit doesn't leak — it just loses output, throws error codes, and eventually needs a heat exchanger that costs a serious fraction of a new unit.

Every month

• Rinse the inlet water filter screen. This is the single most-skipped task and the most common cause of "my tankless suddenly runs cold."
• Check the air intake and exhaust vent terminations outside for nests, leaves, or snow.

Every 12 months (every 6–9 in hard water)

• Descale (flush with vinegar or a descaling solution. Close the hot and cold isolation valves, attach hoses to the service ports, and circulate 3–4 gallons of white vinegar or a commercial descaler with a small submersible pump for 45–60 minutes, then rinse with clean water and restore the valves. If your unit has no isolation valves with service ports, have a plumber add them — it turns a service call into a DIY task forever after.
• Clean the air filter and, on condensing units, check the condensate drain and neutralizer.
• Inspect the burner for soot or yellow flame (gas units) — that's a combustion issue for a pro.
• Note any error codes the unit has thrown during the year before clearing them.

Skip the schedule and expect reduced flow, temperature swings mid-shower, longer waits for hot water, and eventually a lockout code. Manufacturers also commonly require documented annual descaling for the heat exchanger warranty to hold.

If you have hard water

Water hardness is the biggest single variable in how long either type of unit lasts. A $15 test strip tells you where you stand. Above roughly 7 grains per gallon:

• Flush a tank every 6 months instead of yearly.
• Descale a tankless unit every 6–9 months.
• Check the anode rod every 2 years.
• Consider a softener or a scale-inhibiting filter — it pays for itself in appliance life across the water heater, dishwasher, and washing machine together.

Warning signs to stop ignoring

• Rusty or metallic-tasting hot water — the tank lining is failing. This one is terminal.
• Water pooling at the base — a tank seam leak doesn't get better; plan replacement now, not after.
• Rumbling, popping, or banging — heavy sediment. Flush it and see if it improves.
• Hot water running out faster than it used to — sediment volume or a failed lower element.
• The T&P valve discharging on its own — excess pressure or temperature. Treat this as urgent.
• Tankless error codes or mid-shower cold bursts — usually scale or a clogged inlet screen.
• Any smell of gas, or soot around a gas unit — shut it down and call the utility.

Lifespan and when to replace instead of repair

• Gas tank: 8–12 years.
• Electric tank: 10–15 years.
• Tankless: 20+ years with descaling; the heat exchanger is the limiting part.

Replace rather than repair when the unit is past its expected life and the repair runs more than about half the cost of new, when the tank itself is leaking (nothing fixes that), or when you're on a second major repair in two years. Replacement also forces the useful question: an aging tank in a finished space is a strong case for going tankless, or at minimum for adding a drain pan and a water leak sensor.

What a professional service visit should include

Expect $100–200 for a tank service, $150–300 for a tankless descaling:

• Full drain and sediment flush, or a complete descaling cycle
• Anode rod inspection and replacement if depleted
• T&P valve test and thermostat calibration
• Element or burner and flame sensor inspection
• Combustion and venting check on gas units, including draft
• Expansion tank pressure check
• Connection, shutoff, and drain pan inspection

Ask for the anode rod condition and the water hardness reading in writing — those two numbers predict everything that happens next.

Keep the record, not just the memory

Nobody remembers whether they flushed the tank last spring or the spring before. Add your water heater to MaintFolio with the model, serial number, and install date, and the annual flush, anode check, and tankless descaling all schedule themselves — with a service history and receipts attached to the unit for the warranty claim, the next plumber, or the buyer's inspector. Pair it with the HVAC maintenance checklist and your seasonal home maintenance schedule and the mechanical room takes care of itself.

Bottom line: flush a tank yearly, check the anode every three years, descale a tankless unit annually and rinse its inlet screen monthly, and keep the install date written down somewhere you'll find it. Two hours a year against a 50-gallon flood and a decade of lost service life.