Water Heater Element: Testing, Replacing and Sediment Burnout

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Electric tank water heaters are simple machines. A steel tank holds the water, an insulated jacket keeps it warm, and two electric heating elements, each controlled by its own thermostat, do the actual heating. When one of those parts fails, the symptoms are predictable: water that never gets fully hot, showers that turn cold sooner than they used to, or a breaker that trips the moment the heater calls for heat. A failed water heater element is one of the most common causes, and on many tanks it is a replaceable part. This guide explains how upper and lower elements work together, how to read the symptoms, why elements burn out (including the instant failure caused by energizing a dry element), how professionals test and replace them, what replacement options exist, and when an aging tank makes replacing the whole heater the better call. It also includes hedged cost ranges for Front Range homeowners.

Part of our Plumbing & Water guide — start there for the full picture →

How a Water Heater Element Works

A heating element is a metal sheath containing a resistance wire. When the thermostat closes, current flows through the wire, the sheath gets hot, and that heat passes directly into the surrounding water. Most residential electric tanks have two elements:

• The upper element sits a short distance below the top of the tank. It heats the top portion of the water first, which is where hot water is drawn from.
• The lower element sits near the bottom of the tank and does most of the work of heating the bulk of the water once the top is satisfied.

In the most common arrangement, the two elements do not run at the same time. The upper thermostat has priority: when the top of the tank is cold, it powers the upper element. Once the top reaches its set temperature, the upper thermostat switches power down to the lower thermostat, which then runs the lower element until the bottom of the tank is hot. This “non-simultaneous” design keeps the heater’s total current within the capacity of its circuit.

That sequence explains a lot of the symptoms below. The U.S. Consumer Product Safety Commission (CPSC) also notes in its guidance on avoiding tap water scalds that most electric water heaters have two thermostats, both of which must be set to a common temperature for proper operation, and that reaching them requires removing the upper and lower access panels. For more on how those controls work and how to set them, see our guide to the water heater thermostat.

Symptoms of a Bad Water Heater Element

Lukewarm Water That Never Gets Hot

If the upper element fails, the upper thermostat never gets satisfied and never passes power to the lower element. The result is often no hot water at all, or only slightly warm water. If the upper thermostat itself has failed, the symptoms can look similar, which is why testing both parts matters.

Hot Water That Runs Out Fast

If the lower element fails, the upper element still heats the top portion of the tank. The first few minutes of a shower feel normal, then the water turns cool far sooner than it used to because the bulk of the tank is never heated. This is one of the most common complaints and a classic sign of a failed lower element. Our guide to no hot water walks through how to separate element failures from supply, gas and setting problems.

Tripping Breakers

An element whose sheath cracks can let water reach the resistance wire and short to the tank, tripping the breaker as soon as the element energizes. A heater that trips its breaker repeatedly should not be reset again and again. The National Fire Protection Association (NFPA) lists frequent problems with blowing fuses or tripping circuit breakers among the reasons to call a qualified electrician. Shorted elements are one cause, but wiring faults, a failed thermostat or a loose connection can also be responsible. Our guide on a water heater tripping the breaker covers the possibilities in more detail.

Other Clues

• Popping, crackling or hissing sounds from the bottom of the tank, often a sign of sediment around the lower element.
• Hot water that slowly gets less hot over weeks rather than failing suddenly.
• Water pressure and temperature that recover much more slowly after use.
• Discolored or scorched wiring at the element terminals, visible only by a professional with the panel off and power disconnected.

Why Elements Burn Out

Dry Firing: Instant Failure

A water heater element is designed to be surrounded by water at all times. Energizing an element in an empty or partly drained tank is known as dry firing, and it can burn out the element within seconds because there is no water to carry the heat away. Dry firing is a frequent and avoidable mistake after draining a tank for flushing, replacing an element or installing a new heater.

The rule is simple: the tank must be completely full before power is restored. The usual way to confirm this is to open a hot water faucet somewhere in the house while the tank refills and leave it open until water flows steadily with no sputtering air. Only then should the breaker be turned back on.

Sediment Burnout

Hard water carries dissolved minerals that settle to the bottom of a tank as sediment over time. Along much of the Front Range, mineral content is high enough that sediment buildup is a common finding. The lower element sits close to the bottom and can become partly buried in scale and sediment. When that happens, the element cannot transfer heat efficiently to the water, its sheath runs hotter, and it can fail early. Scale also forms directly on element surfaces, insulating them in the same way.

Regular flushing helps remove loose sediment before it builds up around the lower element. Our guide to a water heater flush explains the process and frequency. The anode rod, a sacrificial metal rod that helps protect the steel tank from corrosion, plays a related role in tank longevity; the water heater anode rod guide explains inspection and replacement.

Age, Voltage and Wiring Faults

Elements also wear out with age, and loose wiring at the terminals can overheat connections and damage the element or thermostat. Installing an element with the wrong voltage rating, such as a 120-volt element on a 240-volt circuit, can cause rapid failure.

Testing an Element: Power Off and Verify

Testing and replacing elements involves 240-volt circuits, and the thermostat terminals behind the access panels carry live power whenever the breaker is on. This is not live-circuit work for homeowners. The safe sequence, which a qualified technician or electrician will follow, looks like this:

1. Turn off the breaker serving the water heater, and use a lockout or tag if the panel is out of sight. The CPSC’s scald guidance also tells owners to start by shutting off current to the heater and turning off its circuit breaker or removing its fuse before reaching the thermostats.
2. Verify power is off at the heater with a properly rated voltage tester before touching any terminal. Some heaters are fed by a double-pole breaker, and a mislabeled panel is common.
3. Remove the access panels and push aside the insulation and plastic safety covers.
4. Test the element for continuity or resistance with a multimeter with the wires disconnected. An open reading means the element is broken.
5. Test for a short to ground by checking from each element terminal to the tank or the element’s mounting flange. Any continuity indicates a grounded, failed element.

A homeowner who is comfortable working on de-energized appliances may choose to do steps 1, 3 and 4 after a qualified person has confirmed the method, but anyone unsure should stop at turning off the breaker and call a professional. Never test or adjust parts with the power on.

The Reset Button and High-Limit Cutoff

Most electric tanks also have a high-limit cutoff, often called the ECO (energy cut-off), built into the upper thermostat with a red reset button. It opens and shuts off power to both elements if water in the top of the tank gets too hot. When it trips, the symptom is no hot water at all, which can look like an element failure. Pressing the reset button, which should only be done with the breaker off and by someone comfortable removing the upper panel, may restore heat. A reset that trips again, though, is a warning sign: a thermostat stuck closed or an element shorted to the tank can keep heating water past the set point. Repeated trips call for a professional diagnosis rather than repeated resets, since the cutoff is a safety device and should never be bypassed.

Replacing a Water Heater Element

Element replacement is one of the more common water heater repairs. In outline, the process involves turning off power and verifying it is off, shutting the cold water supply, draining the tank at least below the level of the element (or fully, if flushing at the same time), removing the old element with an element wrench, installing a new element with a fresh gasket, refilling the tank completely and purging air from a hot water faucet, and only then restoring power. The order of the last two steps is what prevents an instant dry-fire failure of the new part.

Element Types and Ratings

• Screw-in elements. Most residential tanks built in recent decades use screw-in elements with a threaded base. Older heaters sometimes use bolt-on or flange-style elements held by bolts.
• Voltage and wattage. Replacements should match the voltage and wattage listed on the heater’s rating plate. Common residential ratings include 3,500 to 5,500 watts at 240 volts, but the rating plate, not a typical value, controls.
• Low watt density. Low-watt-density elements spread the same wattage across a longer sheath, often folded back on itself, so the surface runs cooler. They are frequently recommended for hard-water areas because they tend to tolerate scale and sediment better than standard high-watt-density elements.
• Sheath materials. Copper, stainless steel and specialty-coated sheaths are available, with stainless and coated options often marketed for hard or aggressive water.

It is good practice to replace the gasket every time and to check the thermostat at the same time, since a failed element and a failed thermostat sometimes occur together. Replacing both elements at once is a judgment call; some technicians recommend it on older heaters to avoid a second service call.

Water Temperature and Scald Safety

After an element or thermostat is replaced, both thermostats should be set to the same, safe temperature. The CPSC urges users to lower their water heaters to 120 degrees Fahrenheit, explaining that the majority of tap water scald injuries and deaths involve the elderly and children under five. According to the CPSC, most adults will suffer third-degree burns if exposed to 150-degree water for two seconds, burns also occur with a six-second exposure to 140-degree water or a thirty-second exposure to 130-degree water, and even at 120 degrees a five-minute exposure could result in third-degree burns. The CPSC recommends checking the result by holding a candy or meat thermometer under a faucet. Households with infants, older adults or anyone with reduced sensation should pay particular attention to the setting.

Repair or Replace the Water Heater?

An element is usually an inexpensive part, so replacing one on a sound, mid-life tank is often worthwhile. The decision changes when the tank itself is near the end of its life. Signs that replacement deserves serious consideration include:

• The heater is roughly ten years old or more, or near the end of its warranty term.
• There is rust-colored water, corrosion at fittings or any sign of the tank itself leaking.
• Elements keep failing despite flushing, suggesting heavy sediment or scale.
• Multiple components need replacement at once.

Our guides on water heater lifespan and water heater replacement cost explain typical service life and what goes into a replacement estimate. For homeowners replacing an electric tank, heat pump water heaters are worth a look. ENERGY STAR explains that heat pump water heaters use electricity to move heat from the surrounding air into the water rather than generating heat directly, and that during periods of high hot water demand they automatically switch to standard electric resistance heat, which is why they are often called hybrid water heaters. They still contain an electric element for that backup role, so element care remains relevant.

Typical Costs

Costs vary with the heater, access, local labor rates and whether other repairs are found. These are rough industry estimates for budgeting along the Front Range, not quotes:

• Replacement element (part only): often roughly $20 to $60, more for specialty or low-watt-density elements.
• Professional element replacement: commonly roughly $150 to $350 including labor and drain-down.
• Element plus thermostat replacement: often roughly $200 to $450.
• Professional flush: often roughly $100 to $250, sometimes bundled with an element repair.
• Full tank replacement: varies widely by size, fuel type and code upgrades; see the replacement cost guide linked above.

Water Heaters and the Home Inspection

Water heaters fall squarely within a standard home inspection. The American Society of Home Inspectors (ASHI) Standard of Practice requires inspectors to inspect water heating equipment and hot water supply systems and to describe water heating equipment, including energy sources. A home inspector typically notes the heater’s age from the data plate, looks for leaks, corrosion, temperature and pressure relief valve discharge piping and electrical connections, and may check hot water at fixtures. An inspector will not usually remove element access panels or test elements, so a heater that seems sluggish may warrant a closer look by a plumber or electrician before closing.

For more on inspection scope and choosing an inspector, see our guide to hiring a home inspector and the plumbing and water hub for related water heater and plumbing topics.

References

• Avoiding Tap Water Scalds (Publication 5098) — U.S. Consumer Product Safety Commission
• Electrical Safety in the Home — National Fire Protection Association
• How It Works: Heat Pump Water Heaters — ENERGY STAR
• ASHI Standard of Practice for Home Inspections — American Society of Home Inspectors

Not sure how much life the water heater has left in a home you are buying? Get in touch through our contact page and we can help you find an inspector who will document its age, condition and installation before you close.